U.S. President Donald Trump, who is fighting off allegations of ties between his election campaign and Moscow, said he would invite Russian President Vladimir Putin to the White House but added that now was not the right time for that.

The Republican president drew criticism last week from Democrats who accused him of not pressing Putin hard enough at a meeting they held in Germany over Moscow's alleged interference in the 2016 U.S. presidential campaign.

Accusations that Moscow meddled in the election and colluded with the Trump campaign have dominated Trump's first months in office. Russia denies meddling, and Trump says there was no collusion.

Trump's comments came as he defended his eldest son, Donald Trump Jr., who met with a Russian lawyer during the 2016 presidential campaign after he was told she might have damaging information about Democratic candidate Hillary Clinton.

Trump told Reuters on Wednesday that he did not know about his son's meeting until recently. But in a conversation with reporters later that day, Trump said that "in fact maybe it (the meeting) was mentioned at some point," adding he was not told it was about Clinton.

Trump has said he wants to work with Moscow on issues like Syria, and told reporters travelling with him on Air Force One to Paris that he was open to the idea of inviting Putin to the White House at some point.

"I don’t think this is the right time, but the answer is yes, I would," when asked if he would extend such an invitation to the Russian leader. The comments were released by the White House on Thursday.

'DID YOU DO IT?'

U.S intelligence agencies said earlier this year that Russia sought to help Trump win the election by hacking private emails from Democratic Party officials and disseminating false information online.

Trump said in the Reuters interview on Wednesday that he had asked Putin last week if he was involved in Russian interference in the campaign, spending the first 20 or 25 minutes on that issue during a meeting that lasted more than two hours.

"I said, 'Did you do it?' And he said, 'No, I did not. Absolutely not.' I then asked him a second time in a totally different way. He said absolutely not," Trump said.

Washington this week has been fixated on emails disclosed by Donald Trump Jr., showing him eagerly meeting with lawyer Natalia Veselnitskaya in June last year - the most tangible evidence of a connection between Trump's campaign and Russia, a subject that has also prompted an investigation by a federal special counsel.

Trump Jr. was told by an intermediary that the lawyer had information that was part of Moscow's official support for his father's campaign.

Trump said in Paris on Thursday that nothing of substance came of the meeting.

"My son is a wonderful young man. He took a meeting with a Russian lawyer, not a government lawyer but a Russian lawyer. It was a short meeting. It was a meeting that went very, very quickly, very fast," he said at a news conference with French President Emmanuel Macron.

Trump said it was normal in U.S. politics for campaign teams to look into allegations about their opponents, as his son agreed to do before the meeting in June 2016.

Senate Judiciary Committee Chairman Charles Grassley, a Republican, planned to send a letter on Thursday to the younger Trump to ask him to appear before his committee in a public session, CNN reported.

U.S. House of Representatives Speaker Paul Ryan, the top-ranking Republican in Congress, urged Trump's son to testify.

"I think any witness who's been asked to testify in Congress should do that," Ryan said.

Watchdog groups filed a complaint against Donald Trump Jr., Trump's son-in-law, Jared Kushner, and former campaign chief Paul Manafort on Thursday with the Federal Election Commission, which oversees elections, arguing the three violated the law by meeting with the Russian.