WASHINGTON, United States — One year after American journalist Evan Gershkovich was arrested in Russia on espionage charges, his family vowed Friday to continue fighting for his release, a pledge echoed by President Joe Biden.

"We never anticipated this situation happening to our son and brother, let alone a full year with no certainty or clear path forward," his family said in a letter to the readers of the Wall Street Journal, Gershkovich's employer.

"But despite this long battle, we are still standing strong."

The 32-year-old reporter was detained by Russian security service agents on March 29, 2023, and accused of spying -- the first such charge against a Western journalist since the Soviet-era.

Gershkovich, his employers and the White House all vehemently reject the spying accusations, saying he was an honest journalist doing his job.

"Journalism is not a crime, and Evan went to Russia to do his job as a reporter --risking his safety to shine the light of truth on Russia’s brutal aggression against Ukraine," Biden said in a statement.

He vowed to "continue working every day to secure his release" as well as to "denounce and impose costs for Russia's appalling attempts to use Americans as bargaining chips."

Russian President Vladimir Putin has expressed willingness to exchange Gershkovich, and the Kremlin on Thursday said conversations were still ongoing behind the scenes.

- 'Ache in our hearts' -

In their letter, Gershkovich's parents, Mikhail and Ella, and sister Danielle described the past year as "unimaginable."

"It has felt like holding our breath," the family wrote. "We have been living with a constant ache in our hearts thinking about Evan every moment of every day."

The family, who has met with Biden, thanked the US government, the Journal, Gershkovich's friends and well-wishers for working towards his release and for their support.

"Throughout all the challenges in this tumultuous time we've watched as Evan has faced this uncertainty, stuck in a small cell, with limited news of the world, without his freedom."

The US government has declared that Gershkovich is wrongfully detained, meaning it effectively regards him as a political hostage.

"To Evan, to Paul Whelan, and to all Americans held hostage or wrongfully detained abroad: We are with you. And we will never stop working to bring you home," Biden said, referencing the case of a former US marine also jailed in Russia since 2018.

Democratic and Republican leaders of the bitterly divided US Congress united Friday in calling for Gershovich's release, as well as that of Whelan and others "wrongfully detained" by Russia.

"Journalism is not a crime, and reporters are not bargaining chips," their statement said.

UK Foreign Minister David Cameron called Russia's detention of Gershkovich "a damning indictment of its disregard for media freedom, and the values of truth and objectivity."

Over the past year, Gershkovich's family has watched footage and photographs from a Moscow court where he appeared every few weeks to have his pre-trial detention extended continually.

"We have watched him face this with his head held high because he is innocent," the family wrote in their letter.

This week the court in Moscow ruled that Gershkovich would remain in detention until at least late June.

On Friday, the Wall Street Journal published a large blank space on its front page under the headline: "His story should be here."

At Moscow's Lefortovo prison, the reporter shares a small cell with another inmate.

He gets an hour-long walk in a small prison yard every day, tries to stay fit through exercise and relies on fruit and vegetables sent by friends to supplement the meager prison diet.

"We will continue fighting for Evan's freedom, whatever it takes," the family's letter said.