By Michael Holden and Andy Bruce

MANCHESTER, England (Reuters) - British police are investigating a network in their probe into the Manchester suicide bombing that killed 22 people on Monday, the head of Greater Manchester Police said.

“I think it’s very clear that this is a network that we are investigating,” Chief Constable Ian Hopkins told reporters.

“And as I’ve said, it continues at a pace. There’s extensive investigations going on and activity taking place across Greater Manchester as we speak.”

The Manchester suicide bomber who killed 22 people at a concert venue packed with children had recently returned from Libya, a British minister said, and her French counterpart said he had links with Islamic State and had probably visited Syria as well.

Interior minister Amber Rudd said Salman Abedi had likely not acted alone, and troops were being deployed to key sites across Britain to help prevent further attacks after the official threat level was raised to “critical”.

Rudd also scolded U.S. officials for leaking details about the investigation into the Manchester attack before British authorities were prepared to go public.

British-born Abedi, 22, blew himself up on Monday night at the Manchester Arena indoor venue at the end of a concert by U.S. pop singer Ariana Grande attended by thousands of children and teenagers.