May to chair emergency committee meeting at 0830 GMT - spokesman

British Prime Minister Theresa May will chair a meeting of the government's emergency response committee on Thursday at 0830 GMT, a spokesman for her office said.

May, who is due at a NATO meeting in Brussels later on Thursday, has held several meetings of the committee since a suicide bomber killed 22 people at a concert hall in the northern English city of Manchester on Monday.

UK PM May says terror threat level will remain at critical

British Prime Minister Theresa May said on Thursday the terror threat level will remain at critical, following a suicide bombing at a concert hall in Manchester on Monday.

The threat level was raised to critical, its highest level, on Tuesday, for the first time in 10 years.

"The threat level, as assessed by the independent joint terrorism analysis centre, will remain at critical and the public should remain vigilant," May said following a meeting of the government's emergency response committee.

Manchester attack arrests "significant," important items found - police

British police have made significant arrests and have uncovered important items as they investigate a suicide bomb attack which killed 22 at a music concert in Manchester, the head of the city's police said.

Greater Manchester police are holding eight people in custody, having released a woman without charge on Thursday.

"I want to reassure people that the arrests that we have made are significant, and initial searches of premises have revealed items that we believe are very important to the investigation," police chief Ian Hopkins told reporters.

"These searches will take several days to complete." 

UK security services have thwarted five plots since March Westminster attack - source

British security services have thwarted 18 militant plots in the UK since 2013, including five following an attack in central London in March, a source with knowledge of the matter told Reuters.

"MI5 is managing around 500 active investigations, involving some 3,000 subjects of interest at any one time," the source told Reuters on condition of anonymity.

MI5, established in 1909 to counter German espionage ahead of World War One, is tasked with protecting British national security. Most of MI5's work is focused on counter-terrorism and it employs around 4,000 people.

MI5 is trying foil several plots against Britain at any one time, the source said, adding that the Manchester suicide bomber, Salman Abedi, had been on its radar.

"Abedi was one of a larger pool of former subjects of interest whose risk remained subject to review by MI5 and its partners," the source said.

"Where former subjects of interest show sufficient risk of re-engaging in terrorism, MI5 can consider re-opening the investigation, but this process inevitably relies on difficult professional judgements based on partial information."

British suicide bomber might have made the bomb himself - source

A British suicide bomber who killed 22 people and wounded 116 might have made the bomb himself or with some assistance from an accomplice, a source with knowledge of the investigation told Reuters.

"The focus is still the search for accomplices and the network but he could have made this bomb himself," the source told Reuters.

The source said that while the bomber may have had some assistance it was also possible that he made the bomb himself. Some investigators have feared that an experienced bomb-maker was at large.

Police said on Thursday they had made significant arrests and uncovered important items as they investigate the Manchester suicide bombing.

Greater Manchester police are holding eight people in custody, having released a woman without charge on Thursday.