President Trump responded on Friday to the terror attack inside a London subway car at Parsons Green that left 22 people hospitalized. Trump slammed the "loser terrorist" who detonated the makeshift bomb, but also suggested that those behind the attack had already been on Scotland Yard's radar — an allegation that has sparked strong criticism.

On Friday, a bomb detonated in an eastbound District Line train at Parsons Green, badly burning several people and resulting in a stampede that injured several more. In total, 22 people have been hospitalized. The attacker is believed to still be at large, and officials say the incident is being treated as an act of terror. ISIS has celebrated the attack as a "trial run" for a larger strike.

Trump quickly responded to the horrific incident on Twitter Friday.

"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!"

Trump followed up the tweet by pointing to the attack as another example of why his travel ban from terror-riddled countries needs to remain intact.

"The travel ban into the United States should be far larger, tougher and more specific — but stupidly, that would not be politically correct!" he wrote.

Trump also smacked the Obama administration's feckless campaign against ISIS and called for a more "proactive & nasty" approach to the War on Terror.

"We have made more progress in the last nine months against ISIS than the Obama Administration has made in 8 years. Must be proactive & nasty!" he wrote.

Trump's suggestion that Scotland Yard was already tracking the terrorists behind the attack has received some strong pushback, including from Nick Timothy, the former chief of staff to British Prime Minster Theresa May.

"True or not — and I'm sure he doesn't know — this is so unhelpful from leader of our ally and intelligence partner," he stated, the Daily Mail reports.

One of the most vocal critics of Trump in England, London Mayor Sadiq Khan, whom Trump has slammed for his weak handling of terror, responded to the attack by saying the city condemns terrorism and will "never be intimidated or defeated by terrorism."

"As London has proven again and again, we will never be intimidated or defeated by terrorism," said Khan. "My sincere gratitude goes to all our courageous emergency responders and the TfL staff who were first on the scene. I urge all Londoners to remain calm and vigilant."

After the horrific June attack that resulted in eight people dead and dozens wounded, Trump had smacked Khan for trying to play down the threat by telling citizens there was "no reason to be alarmed" by the police presence.

The terrorist behind the bombing in the subway train at Parsons Green is believed to be at large, the bomb apparently detonated by a timer.

"A hunt for the person who placed the device is under way, with hundreds of detectives and MI5 investigating," BBC reports. "Prime Minister Theresa May condemned the 'cowardly' attack, which she said had 'intended to cause significant harm.'"

"At least one child was hurt after a photo emerged of a schoolgirl with burned legs," Express reports. "Almost half of the injured were hurt in a stampede following the explosion. The rest suffered burns when the homemade device exploded."