British police have arrested a "large part of the network" behind this week's Manchester suicide bombing but more arrests are likely, the country's top counter-terrorism officer said on Friday, May 26, according to Reuters.

Mark Rowley said "immense" progress had been made in the investigation into Salman Abedi, who killed 22 people, seven of them children, at a pop concert in Manchester on Monday.

"They're very significant, these arrests. We're very happy we've got our hands around some of the key players that we are concerned about. But as I say, there is still a little bit more to do," Rowley told broadcasters.

Since the attack, armed police backed up by the army have been patrolling cities and trains. Interior minister Amber Rudd said the official threat risk remained at its highest level, "critical", meaning another attack is expected imminently.

Hospitals have been warned to be ready. However, Security Minister Ben Wallace said there was no evidence of a specific threat over Britain's holiday weekend, when major events will take place including Saturday's soccer FA Cup final in London, where extra armed officers will be on duty.

As campaigning for a national election on June 8 resumed after it was suspended following the attack, the opposition Labour Party, emboldened by its rise in opinion polls, charged that Britain's foreign policy had increased the risk of attacks.

Labour leader Jeremy Corbyn also chided Conservative Prime Minister Theresa May for cutting spending on policing. "We must be brave enough to admit the 'war on terror' is not working," he said.

May hit back. "Jeremy Corbyn has said that terror attacks are our own fault," she said. "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."

May was speaking to reporters at a summit of Group of Seven leaders in Sicily where she won support for action to prevent militants from using the internet to spread propaganda.

A new poll showed Labour had closed the gap with May's Conservatives to 5 points, suggesting a far tighter race than previously anticipated.

Nine people are being held by police following the bombing at the Ariana Grande concert, including a man arrested on Friday evening. A further two people who were arrested earlier in the week have been released.

The Guardian newspaper, without citing sources, said three of the 10 people arrested so far were brothers who were believed to be cousins of the bomber. Abedi's father and two brothers have also been arrested in Britain and in Libya.

Grande, who returned to the United States shortly after Monday's attack, said on Friday she would hold a benefit concert in Manchester for the victims of the bombing.