UK issues warning of another 'imminent' attack, raises threat level from 'severe' to 'critical'

The United Kingdom has deployed security officials to all the important sites in the country to tighten safety measures in the region, as police officials warn of another 'imminent' attack in Britain. The authorities have raised the threat level in the nation from 'severe' to a 'critical' level.

A deadly blast killed at least 22 people and injured more than 59 in Manchester on Monday. A large crowd had gathered at the Manchester Arena for famous US pop singer Ariana Grande's concert. The explosion occurred at the end of a concert, and a suicide bomber was believed to be behind the attack.

UK police on Tuesday said that they believed British-born Salman Abedi, aged 22, carried out Britain's deadliest bombing in nearly 12 years. Prime Minister Theresa May issued a caution saying that another attack in the country could be imminent.

United States security sources, citing British intelligence officials, on Tuesday said that Abedi was born in Manchester to parents of Libyan origin.

The UK PM also said that it was possible that a wide group was associated with the bombing at the crowded concert hall in Manchester, which also killed children. The incident has prompted authorities to heighten security across the country just weeks before the general election.

An independent body, which sets the threat level in Britain, recommended that it be raised to "critical" from "severe" for the first time since June 2007.

"This means that their assessment is not only that an attack remains highly likely but that a further attack may be imminent," May said in a televised statement from her Downing Street Office after a meeting of the government's crisis response committee.

"Armed police officers responsible for duties such as guarding key sites will be replaced by members of the armed forces ... You might also see military personnel deployed at certain events, such as concerts and sports matches."

Extremist group, Islamic State (ISIS), claimed responsibility for Manchester attack and  called it a revenge attack against "Crusaders."