Sir Paul McCartney has appealed to Vladimir Putin to free 30 protesters who have been imprisoned in Russia for two months.
The Beatles legend backed the 28 Greenpeace activists and two journalists who were charged on suspicion of piracy and hooliganism following a protest against oil drilling in the Arctic Ocean.
If they are found guilty, they face up to seven years in prison.
In an open letter posted on his website, the 71-year-old star urged Putin to intervene and reunite the individuals with their families in time for Christmas.
"Vladimir, millions of people in dozens of countries would be hugely grateful if you were to intervene to bring about an end to this affair," he wrote.
"I understand, of course, that the Russian courts and the Russian presidency are separate. Nevertheless, I wonder if you may be able to use whatever influence you have to reunite the detainees with their families."
He continued: "Forty-five years ago I wrote a song about Russia for the White Album, back when it wasn't fashionable for English people to say nice things about your country."
McCartney tweeted his 1.7 million followers: "The Russian ambassador kindly responded saying that their situation is not properly represented in the world media."
"It would be great if this misunderstanding could be resolved and the protesters can be home with their families in time for Christmas.
"We live in hope. Paul McCartney."
Government officials confirmed that the protesters, who were originally detained in the city of Murmansk, had been taken to pre-trial detention centres in St Petersburg, which is easier to get to for family and lawyers.
Greenpeace said that more than two million people had sent letters and emails calling for the "Arctic 30" to be released as fears for their saftey continue to mount.
McCartney previously spoke out against the incarceration of Pussy Riot, two of whom are in jail for their "Putin Prayer" protest in the Cathedral of Christ the Saviour in Moscow in 2012.