A blast went off on a train in Parsons Green station in west London on Friday morning, and it was later reported that the blast was heard as a result of a detonated bomb that had been placed on the train in what British police later confirmed was a "terrorist incident".
"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!" he continued. Asked whether Trump knew something Britain did not, May said: "I never think it's helpful for anybody to speculate on what is an ongoing investigation".
More than 20 people were hospitalized after the explosion..
Downing Street said Mr Trump had offered his condolences over the attack during the telephone call.
The travel ban targeting a handful of Muslim-majority countries has been contentious since the president first proposed it in January.
According to BBC, the explosive device had a timer, but "may have partially failed", which could explain why the attack was not worse. British authorities said the incident is being investigated as a terror attack.
As a presidential candidate, Trump had proposed a blanket ban on all Muslims from entering the United States after the 2015 San Bernardino terrorist attack.
Speaking to LBC, London mayor Sadiq Khan said he had been "too busy this morning to look at my twitter" and had not seen Trump's tweets.
The Department of Homeland Security has been working on a report about countries that USA authorities say do not provide adequate information to vet their travelers. "Perhaps we are not almost tough enough".
The president even linked the attack to his controversial travel ban.
The president wrote: '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!" The Supreme Court is scheduled to hear arguments on October 10 on the legality of the bans on travelers from six mostly Muslim countries and refugees anywhere in the world.