Brussels: President Donald Trump pledged on Thursday that he will "of course" raise the issue of Moscow's interference in the 2016 election at his Monday summit with Russian President Vladimir Putin, but he said he has little recourse if - as expected - Putin denies that Russia interfered.

"Look, he may. What am I going to do? He may deny it," Trump said at a news conference on the second day of a NATO summit. "All I can do is say, 'Did you?' And, 'Don't do it again.' But he may deny it."

US President Donald Trump and Russia\'s President Vladimir Putin talk during the family photo session at the APEC Summit in Danang, Vietnam. Credit:AP

Trump continued to strike a friendly tone toward the Russian leader, calling him a "competitor" rather than a US enemy - while declining to label him as a security threat to the United States or European nations.

"Somebody was saying, is he an enemy? He's not my enemy. Is he your friend? No, I don't know him very much," Trump told reporters on Thursday. "Hopefully, someday, he'll be a friend. It could happen."