Islamic State has claimed responsibility for Saturday night’s attack on London Bridge, which left seven people dead and injured 48, with 21 still in critical condition.

The terror group said just 24 hours after the atrocity was committed in the UK capital city that its fighters carried out the attack and a statement posted on the militant group’s Amaq media agency website said “a detachment of Islamic State fighters executed yesterday’s London attack.”

Twelve people were arrested on Sunday morning in Barking, east London, following a raid at an apartment belonging to one of the three attackers that were shot dead by police on Saturday night.

The Metropolitan Police has said that the investigation into last night’s attack is “progressing rapidly.” Meanwhile, the country’s Prime Minister Theresa May took a tough stance in response to the event this morning, labelling the assailants as copycats “bound together by the single evil ideology of Islamist extremism that preaches hatred, sows division and promotes sectarianism.”

This is the third attack in Britain in as many months: Last month, a suicide bomber killed 22 as crowds were leaving an Ariana Grande concert in Manchester Arena while four were killed after a man drove a car into pedestrians on a sidewalk near the Houses of Parliament in March.