Washington (AFP) - Jason Rezaian, the Washington Post journalist who has been held by Iran's government for nearly 18 months, was allowed a rare visit with relatives for several hours on Christmas Day, the daily said Friday.

The Iranian-American reporter, convicted of espionage by a secretive Iranian court and serving an unspecified prison sentence, marked his 500th day in the notorious Evin prison earlier this month.

"This is the first time in the year that I have been visiting him in Evin prison that I could spend an extended time there and bring him his first home cooked meal in months," his mother Mary Rezaian said in an email to the newspaper.

"We had a wonderful time together reminiscing of holidays past."

Rezaian's wife Yeganeh Salehi, an Iranian citizen who works for a newspaper based in the United Arab Emirates, also attended.

Rezaian, 39, was born in the United States and holds dual nationality. He was arrested in July 2014 at his home in Tehran, where he had worked for the Post for two years.

Salehi was also arrested, but she was released on bail.

The Washington Post's executive editor, Martin Baron, said he and staff were pleased with Iran's "act of basic humanity" in allowing Rezaian to spend time with family.

But Baron reiterated the Post's call for their colleague's release.

"We encourage his jailers in Iran to follow up by doing all that justice and decency require: Release Jason from prison and allow him a return to life as a free man who can spend time with his family where and whenever he pleases," he said.