A suicide bomber blew himself up outside a packed Roman Catholic cathedral on Indonesia’s Sulawesi island during a Palm Sunday Mass, wounding at least 20 people, police said.

A video obtained by the Associated Press showed a burning motorbike at the gates of the Sacred Heart of Jesus Cathedral in Makassar, the capital of South Sulawesi province.

The attack came as Indonesia was on high alert following the arrest of Aris Sumarsono, known as Zulkarnaen, the leader of Jemaah Islamiyah, in December.

Wilhelmus Tulak, a Catholic priest who had been leading the Mass when the bomb exploded at about 10.30am, told reporters that a loud bang shocked his congregation, who had just finished the Sunday service marking the beginning of the Holy Week before Easter.

The first batch of churchgoers were walking out of the church while another group was coming in when the blast happened, he said.

He said security guards had suspected two motorists who wanted to enter the church and confronted them.

One then detonated his explosives and died near the gate. The injured included four guards and several churchgoers.

National Police spokesman Argo Yuwono told a news conference in the capital, Jakarta, that police are still trying to identify two attackers on a motorbike who used powerful explosives.

He said officers are investigating whether they were linked to a local affiliate of the banned Jemaah Islamiyah network or were acting independently.

Around 64 suspects had been detained by Indonesia’s counter-terrorism squad, known as Densus 88, in several provinces, including 19 last month in Makassar. The arrests followed a tip-off about possible attacks against police and places of worship.

Indonesia, the world’s most populous Muslim-majority nation, has been battling militants since bombings on the resort island of Bali in 2002 killed 202 people, mostly foreign tourists.

Attacks aimed at foreigners have been largely replaced in recent years by smaller, less deadly strikes targeting the government, police and anti-terrorism forces and people militants consider as infidels.

A court banned Jemaah Islamiyah in 2008, and the group was weakened by a sustained crackdown. A new threat has emerged in recent years inspired by the Islamic State group’s attacks abroad.

The country’s last major attack was in May 2018, when two families carried out suicide bombings in the second-largest city of Surabaya, killing a dozen people including two young girls whose parents had involved them in one of the attacks.

Police said the father was the leader of a local affiliate of the Islamic State group known as Jemaah Anshorut Daulah.

British police said they had arrested two men on Saturday as they stepped up their efforts to capture a suspected network behind the suicide bomber who killed 22 people in Manchester earlier this week.

Officers used a controlled explosion to gain entry to the address in the north of the city where the latest arrests were made. Detectives are now questioning 11 men over the attack by Salman Abedi at a pop concert in Manchester on Monday.

Some hours later, police cordoned off a large area in the Moss Side area of south Manchester and houses were evacuated with a bomb disposal unit sent to the scene.

A man working in a local shop, who declined to be named, told Reuters he saw three men being taken away from the address.

“As part of an ongoing search at a property in Moss Side an evacuation is currently being carried in the area,” police said in a statement.

While Britain’s most senior counter-terrorism officer said police were confident that they had made “immense” progress and had apprehended a “large part of the network”, extra armed officers will be on duty across the country with security stepped up at some 1,300 events over the long holiday weekend.

Britain remains on its highest threat level of critical, meaning an attack is expected imminently, with the army backing up police and hospitals across the country have told staff to be ready for another incident.

The Times newspaper reported on Saturday that intelligence officers had identified 23,000 jihahist extremists living in Britain.

Earlier this week a source with knowledge of the matter told Reuters the security services were managing 500 active operations involving some 3,000 people who were thought to pose a threat.

However, Assistant Commissioner Mark Rowley, the UK police chief for counter-terrorism, advised people to be vigilant but to “go out as you planned and enjoy yourselves”.

There are a number of high-profile events over the weekend including soccer cup finals in London and Glasgow, and the Great Manchester Run.

While police and politicians have praised communities in Manchester for their reaction to the bombing, Greater Manchester Police Chief Constable said there had been a rise in reported hate crimes, from an average of 28 to 56 incidents on Wednesday.

“We can’t directly link these to the events of Monday night and are continuing to monitor the situation,” he said.

Political campaigning for the June 8 national election which was suspended after the Manchester attack resumed on Friday with the bombing becoming a central feature.

The opposition Labour Party, emboldened by a rise in opinion polls, argued that Britain’s foreign policy had increased the risk of attacks and criticised Conservative Prime Minister Theresa May for cutting spending on policing.

May said Labour leader Jeremy Corbyn was saying Britain was to blame for the bombing.

“I want to make one thing very clear to Jeremy Corbyn and to you, and it is that there can never, ever be an excuse for terrorism,” she said at a summit of Group of Seven leaders in Sicily.

A poll on Thursday put May’s Conservatives five points ahead of Labour suggesting a far tighter race than previously anticipated.