More than two million Muslims gathered at Mount Arafat on Monday for a vigil to atone for their sins and ask God’s forgiveness as the annual haj pilgrimage in Saudi Arabia reached its climax.

Pilgrims clad in white robes signifying a state of purity spent the night in an encampment around the hill where Islam holds that God tested Abraham’s faith by commanding him to sacrifice his son Ismail and Prophet Mohammad gave his last sermon.

Other worshippers praying in the nearby Mina area ascended in buses or on foot from before dawn as security forces directed traffic and helicopters and surveillance drones hovered overhead.

Some pilgrims carried umbrellas to protect themselves from the sun as temperatures surpassed 40 degrees Celsius (104 degrees Fahrenheit) after an evening of thunderstorms and high winds. Men and women from 165 countries gathered side by side, while soldiers handed out bottled water and some people snapped selfies.

Pakistani pilgrim Mohamed Forqan, 30, said it was a great day to be a Muslim. “Here in Arafat we feel that we are born today asking Allah to forgive our sins,” he said.

Hilal Issa, 70, from Algeria, said he was praying for God to pardon all Muslims and save the Arab world from its afflictions.

Saudi Arabia has said more than 2.3 million pilgrims, mostly from outside Saudi Arabia, have arrived for the five-day ritual, a religious duty once in a lifetime for every able-bodied Muslim who can afford the journey.

The pilgrims will spend the day on Mount Arafat. By sunset they will move to the rocky plain of Muzdalifa to gather pebbles to throw at stone columns symbolising the devil at another location called Jamarat on Tuesday, which marks the first day of Eid al-Adha, or the feast of sacrifice.

A new kiswa, the cloth embroidered with verses from the Koran, was placed over the Kaaba in Mecca’s Grand Mosque late on Sunday. Pilgrims will return to pray there at the end of haj.

CALLS FOR UNITY

In a haj message, Ayatollah Ali Khamenei, leader of Saudi-rival Iran, called for unity among Muslims as a defence against foreign enemies.

“Muslims should be vigilant about America’s malicious war-mongering policy aimed at Muslims killing Muslims,” he said in comments read by a representative on Iranian television.

The United States reimposed economic sanctions on Iran this month after pulling out of a 2015 international deal aimed at curbing its nuclear programme in return for easing sanctions.

Washington has said Tehran’s only chance of avoiding the sanctions would be to accept President Donald Trump’s offer to negotiate for a tougher nuclear deal, which Iranian officials have rejected.

In a midday sermon, senior Saudi cleric Sheikh Hussein bin Abdulaziz Al al-Sheikh also urged pilgrims to come together with their co-religionists but cautioned: “Haj is not a place for slogans and parties.”

Saudi Arabia stakes its reputation on its guardianship of Islam’s holiest sites – Mecca and Medina – and organising the pilgrimage.

The world’s largest annual gathering of Muslims has in the past seen stampedes, fires and riots, with authorities sometimes struggling to respond. A crush in 2015 killed nearly 800 pilgrims, according to Riyadh, although counts by countries of repatriated bodies showed over 2,000 may have died, more than 400 of them Iranians.

Officials say they have taken all necessary precautions this year, with tens of thousands of security forces and health workers on hand to maintain safety and provide first aid.

Pilgrimage is also the backbone of a plan to expand tourism under a drive to diversify the kingdom’s economy away from oil. The haj and year-round umrah generate billions of dollars in revenue from worshippers’ lodging, transport, fees and gifts.

Officials aim to increase the number of umrah and haj pilgrims to 15 million and 5 million respectively by 2020, and hope to double the umrah number again to 30 million by 2030.

Saudi authorities deployed drones to watch over nearly 2 million pilgrims as they ascended Mount Arafat at the climax of the haj pilgrimage on Sunday, part of stepped up efforts to avoid a repeat of last year’s crush.

In one of the deadliest disasters to befall the annual Muslim rite in decades, the crush killed nearly 800 pilgrims, according to Riyadh, though counts by countries of repatriated bodies showed over 2,000 people may have died, more than 400 of them Iranians.

Chanting “here I am at thy service, O Lord,” the faithful climbed the craggy hills outside Mecca where Islam holds that God tested Abraham’s faith by commanding him to sacrifice his son Ismail and the Prophet Mohammed gave his last sermon.

“I have prayed to God to have mercy on us, give us relief and resolve Syria’s crisis,” said Um Fadi, wearing a traditional long black embroidered dress and head scarf native to her home in southern Syria.

“From the bottom of my heart, I pray that God will lift this agony from Syria and its people,” she added.

Saudi Arabia has said that 1.85 million pilgrims, most of them from outside Saudi Arabia, have arrived for the annual pilgrimage, a religious duty for every able-bodied Muslim who can afford the journey.

Saudi Arabia stakes its reputation on its guardianship of Islam’s holiest sites and organising haj, a role that Iranian authorities have challenged this week as part of an escalating war of words over the handling of last year’s disaster.

The Grand Mufti, the kingdom’s top religious authority, warned Iran on Sunday that to disrupt the haj would be unacceptable, in comments reported by local daily al-Okaz.

“Any policy that aims to divert the haj from its proper course is un-Islamic and is a criminal policy,” he was quoted as saying.

Earlier in the week, Iran’s supreme leader accused Saudi authorities of murdering pilgrims during last year’s crush. In response, Saudi Arabia’s mufti said Iran’s leaders were not Muslims.

Pilgrims from Iran are not attending haj this year, after talks between the two Middle East powers over haj arrangements broke down in May.

The 2015 crush, in which two large groups of pilgrims arrived together at a crossroads in Mina, a few kilometres east of Mecca, on their way to performing the “stoning of the devil” ritual at Jamarat, was the worst disaster to strike the annual pilgrimage for at least 25 years.

The Saudi authorities redesigned the Jamarat area after two stampedes, one in 2004 and one in 2006, killed hundreds of pilgrims, and the frequency of such disasters has greatly reduced as the government spent billions of dollars upgrading and expanding haj infrastructure and crowd control technology.

The haj ministry has said it had prepared a strict timetable for pilgrims from various countries to follow when leaving and returning to their accommodation.

Authorities have also deployed drones to reinforce a network of electronic surveillance of the crowds that would alert authorities to intervene quickly if necessary.

Saudi state news agency SPA said that Crown Prince Mohammed Nayef bin Abdul-Aziz, who is also the interior minister, supervised oversight as pilgrims used buses, trains and private cars to move from their encampments in Mena to Mount Arafat.

So far, things have proceeded smoothly, SPA added.

The pilgrims will spend the day on the mountain and move by sunset to the rocky plain of Muzdalifa, where they will gather pebbles to stone columns symbolizing the devil at another location called Jamarat on Monday, which marks the first day of Eid al-Adha

Iran said on Sunday its pilgrims would not attend the annual Muslim haj pilgrimage, blaming regional rival Saudi Arabia for “sabotage” and failing to guarantee the safety of pilgrims.

Saudi Arabia, which oversees the pilgrimage to Mecca by more than two million Muslims from around the world, accused Iran of effectively depriving its citizens from the religious duty by refusing to sign a memorandum reached after talks with Iran’s Haj and Pilgrimage Organisation.

Relations between the two Gulf powers plummeted after hundreds of Iranians died in a crush in last year’s haj and after Riyadh broke diplomatic ties when its Tehran embassy was stormed in January over the Saudi execution of a Shi’ite cleric.

The dispute has provided another arena for discord between the conservative Sunni Muslim monarchy of Saudi Arabia and the revolutionary Shi’ite republic of Iran, which back opposing sides in Syria and other conflicts across the region.

“Due to ongoing sabotage by the Saudi government, it is hereby announced that … Iran’s pilgrims have been denied the privilege to attend the haj this year, and responsibility for this rests with the government of Saudi Arabia,” Iran’s Haj and Pilgrimage Organisation said in a statement carried by state media.

Saudi media earlier said an Iranian delegation had left the kingdom without an agreement over the haj, the second time the two countries have failed to reach a deal.

Saudi Arabia has blamed Iran for the impasse.

“Saudi Arabia does not prevent anyone from performing the religious duty,” Saudi Foreign Minister Adel al-Jubeir said at a news conference with visiting British Foreign Secretary Philip Hammond.

“Iran refused to sign the memorandum and was practically demanding the right to hold demonstrations and to have other advantages … that would create chaos during haj, which is not acceptable,” he added.

Iranian Culture Minister Ali Jannati said the issue of ensuring the safety of the pilgrims was paramount for Tehran following the death of hundreds of Iranian pilgrims last year.

“The Saudi government deliberately acted in a way to prevent Iranian pilgrims from … attending haj this year,” Jannati told Iran state television.

Eight months after the last haj, Saudi Arabia has still not published a report into the disaster, at which it said over 700 pilgrims were killed, the highest death toll at the annual pilgrimage since a crush in 1990.

Iran boycotted the haj for three years after 402 pilgrims, mostly Iranians, died in clashes with Saudi security forces at an anti-U.S. and anti-Israel rally in Mecca in 1987.