A massive manhunt is underway in London following a blast on a packed subway train early Friday during rush hour that left 22 people injured. Police are calling it a terrorist incident caused by a homemade bomb. So far there have been no arrests.

The explosion occurred about 8:20 AM local time at Parsons Green Tube station.

Downing Street tweeted a message from Prime Minister Theresa May, in which she said “My thoughts are with those injured at Parsons Green and emergency services who are responding bravely to this terrorist incident.”

President Donald Trump responded in a series of tweets, which were not received positively by London authorities.

“Another attack in London by a loser terrorist,” Trump tweeted. “These are sick and demented people who were in the sights of Scotland Yard. Must be proactive!”

A police spokesman told CNN that Trump’s comment is “pure speculation given we don’t know who is involved. Any speculation is unhelpful.”

May also rebuked Trump following a meeting of the Government’s Cobra emergency committee, according to the Independent, saying: “I never think it’s helpful for anybody to speculate on what is an ongoing investigation.”

Trump also called for the Internet to be “cut off” as a recruitment call for terrorists.

This is the latest attack in or around London this year. In March, five people were killed and 40 injured near Parliament when a knife-wielding man went on a rampage, plowing a car into pedestrians on Westminster Bridge, then stabbing a police officer to death. There also was an attack near a mosque in Finsbury Park in north London, and a May suicide bomb attack at Manchester Arena which left 22 dead.