WASHINGTON — President Donald Trump called Friday for a “tougher and more specific” U.S. travel ban after a homemade bomb exploded on a London train.

In several tweets, Trump called the explosion another attack “by a loser terrorist” and suggested London police missed an opportunity to prevent it. He added that his travel ban targeting six mostly Muslim nations should be “far larger, tougher and more specific – but stupidly, that would not be politically correct!”

The bomb exploded on a packed train during rush hour on Friday, leaving at least 22 people injured but no one seriously hurt. Police said the explosion was a terrorist attack, the fifth in Britain this year.

“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!”

Another attack in London by a loser terrorist.These are sick and demented people who were in the sights of Scotland Yard. Must be proactive! — Donald J. Trump (@realDonaldTrump) September 15, 2017

Loser terrorists must be dealt with in a much tougher manner.The internet is their main recruitment tool which we must cut off & use better! — Donald J. Trump (@realDonaldTrump) September 15, 2017

The travel ban into the United States should be far larger, tougher and more specific-but stupidly, that would not be politically correct! — Donald J. Trump (@realDonaldTrump) September 15, 2017

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! — Donald J. Trump (@realDonaldTrump) September 15, 2017

Scotland Yard said it would not comment Trump’s suggestion that police could have prevented the attack. The White House did not immediately respond to a request for comment.

The president has repeatedly criticized London Mayor Sadiq Khan, the British capital’s first Muslim leader.

In June, after attacks in the London Bridge area that claimed seven lives, Khan warned locals not to be alarmed by the large presence of armed officers on the capital’s streets. Trump accused the mayor on Twitter of suggesting there was “no reason to be alarmed” by the attack itself.

On Friday, Trump again jumped into the fray, suggesting that only he could handle extremist militants and that the government should cut off the internet to such groups.

“Loser terrorists must be dealt with in a much tougher manner. The internet is their main recruitment tool which we must cut off & use better!” And he argued that his administration has “made more progress in the last nine months against ISIS than the Obama Administration has made in 8 years.”

Trump concluded: “Must be proactive & nasty!”