British Prime Minister Theresa May criticized President Trump's response to a terrorist attack at a London Underground station, saying he shouldn't speculate on the investigation.

"I never think it is helpful for anyone to speculate in what is an ongoing investigation," May told reporters in London.

"As I've just said police and security services are working to discover the full circumstances of this cowardly attack and to identify all those responsible."

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A device exploded at London's Parsons Green train station on Friday, injuring commuters. British authorities said the incident is being investigated as a terror attack.

Trump responded to the incident on Twitter, blaming it on terrorists and making the case for his travel ban on visitors from six Muslim-majority countries.

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

May's comments came after Trump said he would call May.

This is not the first time Trump has rapidly issued tweets in the wake of a terror attack in the United Kingdom.

Shortly after an attack in central London last June, in which a driver struck several people on London Bridge, the president took to Twitter.

We must stop being politically correct and get down to the business of security for our people. If we don't get smart it will only get worse — Donald J. Trump (@realDonaldTrump) June 4, 2017

Do you notice we are not having a gun debate right now? That's because they used knives and a truck! — Donald J. Trump (@realDonaldTrump) June 4, 2017

At least 7 dead and 48 wounded in terror attack and Mayor of London says there is "no reason to be alarmed!" — Donald J. Trump (@realDonaldTrump) June 4, 2017

London Mayor Sadiq Khan criticized Trump for the tweets and called on the British government to rescind an invitation for the president to visit the country.