Russia's ambassador Sergey Kislyak was all smiles as he glad-handed US lawmakers gathered on Capitol Hill to hear President Donald Trump's maiden speech to Congress, AFP reports.

Two days later he was at the heart of a very Washington scandal, after Trump's newly-appointed Attorney General Jeff Sessions was accused of lying about meeting with the Kremlin's envoy.

Fellow diplomats told AFP that Kislyak, a veteran of many years of US-Russian diplomatic rivalry, would be amused by the spat, the latest to trouble Trump's efforts to form a government.

The 66-year-old engineering graduate has been at the heart of the Moscow foreign policy establishment since the days of the United States and the Soviet Union's Cold War stand-off.

Married and with one adult daughter, he is coming towards the end of what has been an eight-year stint in Washington marked by spy scandals, a failed "re-set" in ties and now political intrigue.

Already, one member of Trump's top team -- short-lived national security adviser Mike Flynn -- has been forced to resign after controversy over his contacts with Kislyak.

Now Sessions has been forced to recuse himself from any investigation related to the Trump campaign -- whose ties with Russia are under scrutiny from all sides -- after he admitted to two encounters with Kislyak in the run-up to the vote.