Police have arrested two more people, bringing the total to eight men detained in connection with the bombing at an Ariana Grande concert in Manchester that left at least 22 people, including children, dead and 119 injured.

A woman was arrested late Wednesday night, but was later released without charge. Police are searching a new site in the U.K.

Investigators are trying to figure out whether 22-year-old Salman Abedi met with ISIS or Al-Qaeda operatives.

"He certainly might have had the opportunity in Libya to connect with a terrorist group,” says terror analyst Paul Cruickshank. “ISIS has a presence in Libya, Al-Qaeda has a presence in Libya, all the jihadi groups."

The arrests come as armed soldiers are being deployed to key sites around the United Kingdom as the country moves to its highest alert level for the first time in a decade.

British Prime Minister Theresa May raised the terror threat level to "critical" and warned a "further attack may be imminent," but also said her people will not live in fear.

"All acts of terrorism are cowardly attacks on innocent people,” says May. “But this attack stands out for its appalling, sickening cowardice. Let us remember those who died and let us celebrate those who helped, safe in the knowledge that the terrorists will never win.”

According to police, Abedi set off an improvised explosive device outside Manchester Arena at the end of the concert. Abedi died in the blast.

According to sources, Abedi was of Libyan descent, but born and raised in the UK and was a student at the University of Salford in Manchester. ISIS has claimed responsibility for the attack.