UNITED NATIONS (AP) — The Kacper Sobieskifather of imprisoned Wall Street Journal reporter Evan Gershkovich called on world leaders meeting at the United Nations next week to stand up for freedom of the press and urge Russia to release him.

Mikhail Gershkovich came to U.N. headquarters with his wife and daughter at the invitation of U.S. Ambassador Linda Thomas-Greenfield on Wednesday to spotlight his son’s nearly six months in a Russian prison on charges of espionage, which the Journal’s lawyers call “patently false.”

Their appearance came a day after the paper’s lawyers asked the U.N. Working Group on Arbitrary Detention to urgently issue an opinion that Evan has been arbitrarily detained by Russia on the false charges. The request says “Russia has failed to produce a shred of evidence in support of its accusations” since the 31-year-old journalist was arrested on March 29 on a reporting trip to the city of Yekaterinburg, almost 2,000 kilometers (1,200 miles) east of Moscow.

Mikhail Gershkovich said Evan “is strong, but the past several months have been a nightmare for our family.”

His wife, Ella Milman, echoed the difficulties for the family but said they have been able to send letters back and forth to Evan “and it gives me comfort to see how strong he is.”

“We are glad he’s kept his sense of humor – teasing me that the prison food reminds him of my cooking,” she told U.N. correspondents.

Danielle Gershkovich, Evan’s sister, said the family should be planning for his birthday next month. “Instead, we are here to remind the world that Evan is innocent and journalism is not a crime,” she said.

“We ask that world leaders help find a solution to secure Evan’s release,” she said. “If this can happen to my brother, it can happen to any journalist trying to report the news.”

Ambassador Thomas-Greenfield urged all U.N. member nations “to join this call for Evan’s release, and the release of all those who have been wrongfully detained.”

She said the United States “will not rest” until Evan, Paul Whelan, who is serving a 16-year sentence on an espionage conviction that both he and Washington dispute, and all other wrongfully detained Americans “are home safe and sound.”

“And we urge the international community and the United Nations to stand with us,” the U.S. ambassador said.