Washington: Russia's ambassador to Washington was overheard by US spy agencies telling his bosses that he had discussed campaign-related matters, including issues important to Moscow, with Jeff Sessions during the 2016 presidential race.

Both The Washington Post and Reuters sources confirmed that ambassador Sergei Kislyak held two conversations with Mr Sessions, then a key foreign policy adviser to Republican candidate Donald Trump, that were intercepted by US intelligence agencies.

One US official told Reuters there was nothing inappropriate about Mr Sessions, at the time a US senator and Trump supporter, discussing policy matters or even Mr Trump's thinking with a foreign diplomat.

"The question is whether he crossed the line and discussed classified information or talked about deals like lifting sanctions if the Russians were interested in investing in the US or had dirt on (Democratic presidential candidate Hillary) Clinton," a second official said. "His memory is another matter."