LONDON (Reuters) - British Prime Minister Theresa May said on Friday it was not helpful for anyone to speculate on investigations after U.S. President Donald Trump tweeted that the culprits behind a train bombing had been  in the sights  of the police. Soon after 22 people were injured in the attack on a busy underground train in west London, Trump tweeted:  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!  His comments appeared to point the finger at British police. 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 . Others chimed in, with May s former chief of staff, Nick Timothy, saying Trump s comment was  so unhelpful from leader of our ally and intelligence partner . London and Washington have long boasted of their  special relationship , close ties that were strained earlier this year when the United States leaked information on an investigation into a bomber who killed 22 at a Manchester pop concert. Trump told reporters after his tweet that he had been briefed on the London incident, and he also said he would be speaking with May, although it was not clear whether his reference to Scotland Yard came up on the call. A senior U.S. government official cast doubt on whether Trump was privy to information over whether the bomber in the west London attack was known or not. The official said that at this point, U.S. agencies had no information to back up any suggestion by Trump that Britain had advance warning or specific intelligence on the attack. At a White House briefing ahead of next week s U.N. General Assembly meeting, Trump s national security adviser, H.R. McMaster, said the president was referring generically to British efforts to combat terrorism and was not making a reference to any specific knowledge authorities in London may have had.  I think he means generally that this kind of activity is what we re trying to prevent, and so these organizations that are responsible for it, whatever comes out of this investigation, that remains to be seen,  McMaster said. Hours after Trump s tweet, Sky News cited security sources as saying they had identified a suspect in the attack, with the help of surveillance footage. 