WASHINGTON (AFP) - United States President Joe Biden met on Wednesday (March 30) with the parents of a former US Marine imprisoned in Russia and promised to work to end the "nightmare" of his detention, the White House said.

US citizen Trevor Reed is serving a nine-year prison term in a penal colony some 500km south-east of Moscow after being convicted of assaulting police officers while drunk in 2019.

"President Biden met today with Joey and Paula Reed, the parents of Trevor Reed, who is wrongfully detained in Russia," presidential spokesman Jen Psaki said in a statement.

"During their meeting, the President reiterated his commitment to continue to work to secure the release of Trevor, Paul Whelan and other Americans wrongfully held in Russia and elsewhere."

"We understand the pain felt by all of Trevor's families and friends enduring the nightmare of his absence, which we are committed to bringing to an end."

A spokesman for Reed said Tuesday that the former Marine was "back on hunger strike and back in solitary", according to a statement posted on Twitter.

Reed had announced a hunger strike on Nov 4, which lasted for two weeks, saying he had been repeatedly placed in an isolation cell for allegedly breaking prison rules.

He denied any wrongdoing.

Diplomatic tensions between Washington and Moscow have soared since Russia invaded Ukraine.

US State department spokesman Ned Price said that US diplomats are being denied access to Americans being held by Russia.

Those include Reed and Paul Whelan, who are being held on what the US says are false or trumped-up charges.

Another American held is professional basketball Brittney Griner, who was detained in Moscow airport on Feb 17 on charges of carrying vape cartridges that contained cannabis oil in her luggage.

Washington fears she will be used as a pawn in the Ukraine dispute and has so far kept a low profile in her case.