MANCHESTER, England — Britain reduced its terrorism threat level a notch, from “critical” to “severe” on Saturday, as authorities said they had made major progress in unravelling the plot behind the Manchester concert bombing.

ManchesterBut police said more arrests were expected, and security was tight across Britain as hundreds of thousands of people attended major soccer matches, concerts and other big holiday-weekend events.

Police made two more arrests in Manchester on Saturday on suspicion of terrorism offenses, bringing the number of suspects in custody to 11. All are men, aged between 18 and 44. In addition, Manchester bomber Salman Abedi’s father and younger brother are in detention in Libya.

British Prime Minister Theresa May said “a significant amount of police activity” and several arrests had led to the level being lowered. But she urged Britons to remain vigilant and said soldiers would remain at high-profile sites throughout the holiday weekend. The troops will gradually be withdrawn beginning on Monday, she said.

A severe threat means an attack is “highly likely,” according to the scale set by Britain’s Joint Terrorism Analysis Centre. Until it was raised Tuesday, it had stayed at severe since mid-2014.

Assistant Commissioner Mark Rowley, Britain’s top counterterrorism police officer, said authorities have dismantled a “large part” of the network around Abedi, who killed 22 people and wounded dozens by bombing an Ariana Grande concert Monday in Manchester.

But he said there were still “gaps in our understanding” of the plot, as investigators probed Abedi’s potential links to jihadis in Britain, Europe, Libya and the Middle East.

Source: usatoday