LONDON — British police made two more arrests and stormed three more locations Sunday as they hunted for suspects in the Manchester bombing, while a government minister said members of attacker Salman Abedi’s network may still be at large.

Greater Manchester Police said two men — one 25 years old and the other 19 — were arrested in the city on suspicion of terrorist offenses. Eleven other men between the ages of 18 and 44 also were in custody.

Most of the searches and arrests since Monday night’s bombing have been in multi-ethnic south Manchester, where Abedi — the son of Libyan parents — was born and raised.

Police say that 1,000 people are working on the investigation, trying to track down Abedi’s accomplices and piece together his movements in the days before he detonated a bomb at an Ariana Grande concert. The explosion killed 22 people — including seven children under 18 — and injured more than 100.

Abedi died in the blast. Investigators say they have dismantled a large part of his network, but expect to make more arrests.

“The operation is still at full tilt,” Home Secretary Amber Rudd said, adding that some suspects could remain at large.

“Until the operation is complete, we can’t be entirely sure that it is closed,” she said.

British police now have 13 suspects in custody — including Abedi’s elder brother Ismail — and have searched properties across Manchester, a city in northwest England. Another brother and Abedi’s father have been detained in Libya.

Police have released surveillance-camera images of Abedi on the night of the attack that show him dressed in sneakers, jeans, a dark jacket and a baseball cap. The straps of a backpack are visible on his shoulders.

Authorities are appealing for more information about his final days. They say he returned to Britain from Libya on May 18, and likely completed assembling his bomb at a rented apartment in central Manchester.

There were prayers for the victims at church services across Manchester on Sunday. In Rome, Pope Francis led thousands of people in St. Peter’s Square in prayer, saying he was “close to the relatives and all those who are weeping for the dead.”

On Saturday, Britain lowered its official terrorism threat level from “critical” to “severe” after police said they had dismantled a large part of Abedi’s network.

But security remained high at major events across Britain on Sunday, including the Great Manchester Run road race, where police armed with submachine guns protected thousands of participants and spectators.

Peter Hook, a member of seminal Manchester band New Order, was among the runners and said the tragedy had brought people together.

“I’ve always had a pride in this city, ever since I was born,” he said. “They picked the wrong people to mess with this time.”

The government is facing criticism after acknowledging that Abedi was on security services’ radar, but wasn’t a major focus of scrutiny.