(CNN)US citizen Paul Whelan, who was arrested in Russia on suspicion of espionage, has filed an appeal against a Moscow court's decision to detain him without bail.
Moscow's Lefortovo court received the appeal from Whelan's lawyer on Thursday, the court's press service told state news agency TASS on Thursday.
"The lawyer's appeal against the ruling to place Whelan in custody has been lodged with the court. The date of consideration has not been fixed," said Yekaterina Krasnova, a spokeswoman for the court.
Whelan's lawyer, Vladimir Zherebenkov, said on January 3 that he filed a complaint with the Lefortovo court because the detention without bail is "excessive and unwarranted."
Whelan, who is also a citizen of the United Kingdom, Ireland and Canada, was arrested December 28 by Russia's Federal Security Service (FSB). If convicted he faces up to 20 years in a Russian jail.
The 48-year-old's family rejects Russia's accusation, asserting Whelan was only in the country for a vacation.
Whelan's twin brother David wrote in an op-ed in Friday's Washington Post that his brother is not a spy. "He is many things to many people, but he is not a spy," he wrote.