British Prime Minister Theresa May said Monday that the country’s terror threat level will remain at “severe” after weekend attacks in London left seven dead and nearly 50 others injured.

May described the assault as an attack on the free world.

"It is now clear that, sadly, victims came from a number of nationalities. This was an attack on London and the United Kingdom, but it was also an attack on the free world,” she said in an interview with BBC.

May said police have identified all the London Bridge attackers and that 11 people remain in custody for possible connections to the attack. Police said attackers would be identified when it is “operationally possible.”

The Islamic State claimed responsibility for the attack through its propaganda wing Amaq News Agency, the SITE intelligence group said Sunday.

The terror network reportedly claimed a "detachment" of its fighters crashed a rented van into a crowd of people on London Bridge before going on a stabbing rampage Saturday night. However, ISIS gave no evidence to back up its claim.

At least 21 people remained in critical condition after the attacks.

London police said that one British Transport police officer and three Metropolitan police officers were injured during the weekend attacks.

The two Metropolitan police officers were on duty during the attack. One a plain clothes officer who received stitches to a head injury and a uniformed officer received an injury to his arm.

One off-duty officer remains in the hospital and in serious condition.

Fox News’ Patrick Manning and the Associated Press contributed to this report.