Donald Trump, the US president, on Sunday admitted that his son met a Russian lawyer in Trump Tower in 2016 to collect information on Hillary Clinton but said it was “totally legal”.

The Sunday morning tweet is Mr Trump's most direct acknowledgement that the motive for the June 2016 meeting was to get dirt on Hillary Clinton, his Democratic rival for the presidency.

It follows reports in American news outlets that the president was becoming concerned that Robert Mueller’s investigation into Russian interference in the election was closing in on family members – particularly Donald Trump Jnr.

As he has in the past, Mr Trump insisted he did not know at the time about the meeting between his son Donald Jnr and Natalia Veselnitskaya, a lawyer with links to the Kremlin.

“This was a meeting to get information on an opponent, totally legal and done all the time in politics - and it went nowhere,” he wrote. “I did not know about it!”