The Islamic State claimed responsibility for Friday morning's terror attack aboard a London train.

The terrorist group took credit for the attack through its Amaq News Agency, which reported a "detachment" from the Islamic State carried out the bombing, according to the SITE Intel Group.

BREAKING: #ISIS issued a formal communique for the #LondonExplosion, reporting 30 wounded pic.twitter.com/2l3NogSCJ2 — SITE Intel Group (@siteintelgroup) September 15, 2017

#ISIS claimed credit for the #LondonExplosion through its 'Amaq News Agency, stating that a "detachment" from its group is responsible pic.twitter.com/mnIJyLJXdG — SITE Intel Group (@siteintelgroup) September 15, 2017

A bucket bomb detonated aboard a London Underground train at the Parsons Green station in southwest London during rush hour Friday morning. At least 29 people were injured.

Police declared the attack a "terrorist incident."

No arrests have been made yet, but London Mayor Sadiq Khan said there is a manhunt underway for the perpetrator.

British Prime Minister Theresa May said the threat level in the United Kingdom was raised from severe to critical in the wake of the explosion, meaning a terror attack is "expected imminently."

"Terrorism is a great challenge of our times, but by standing together, we will defeat it," May said.

Theresa May says UK terror threat level raised to critical, highest possible level, after London Tube blast https://t.co/HCBPJZo8XY pic.twitter.com/liMAODY2IV — BBC Breaking News (@BBCBreaking) September 15, 2017

May spoke with President Trump on Friday, and the president offered his sympathies and prayers for those injured. Trump also pledged the U.S. would continue working with the United Kingdom to combat extremism and "stop attacks worldwide targeting innocent civilians," the White House said.