The Islamic State group on Friday claimed responsibility for the attack on a train in London, in which at least 29 people were injured. Prime Minister Theresa May called the strike cowardly and raised the threat level in the United Kingdom from severe to critical, which means authorities believe that another attack is imminent, CNN reported.

Assistant Commissioner of the London Metropolitan Police Mark Rowley said it was “routine” for the terror group to claim they were behind attacks carried out in “these sorts of circumstances”. The Islamic State group claimed they were behind the tube incident through its Amaq news agency, though without proof.

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A hunt is on for the suspect who placed an improvised explosive device at the Parsons Green station. Specialist officers are securing what is left of the explosive, which May said was “intended to cause significant harm”, BBC reported. The strike is being investigated as a terror attack.

The London Ambulance Service said none of the injuries commuters sustained were serious or life-threatening. Local authorities said most of the injuries seemed to have been caused by flash burns.