Four Russian bikers have been detained in Iraq, possibly on suspicion of spying, prompting a surge of concern at home.

The Russians — who were riding their motorcycles through Iraq on a Central Asia-Middle East road trip — were stopped as they approached Baghdad on Sunday and apparently taken into custody at an Iraqi military base, news reports said Thursday.

The bikers have been severely beaten, accused of espionage and visa forgery, and threatened with the death penalty, said Alexander Orlov, a member of the Moscow-based motorcycle club RAMCC, who said he is in continual contact with the men and a Russian diplomat in Iraq.

"They are among the most experienced motorcycle tourists in Russia," he said, speaking to RIA-Novosti. "They have crossed the whole world. … The speculation that they forged the visas is mere nonsense."

The Russian Embassy in Baghdad declined to provide details about the detentions, saying it did not want to hamper the bikers' release. "Our ambassador has discussed this at a meeting with [Iraq's] leadership," said embassy spokesman Sergei Cherkasov, Interfax reported.

But in a separate interview with NTV television he said the embassy's efforts had been complicated by Iraqi authorities' distraction with international talks on Iran's disputed nuclear program, which are being held in Baghdad this week.

The detained bikers — Oleg Kapkayev, Alexander Vardanyants, Oleg Maximov and Maxim Ignatyev — had been taking a trip across Central Asia, Turkey, Iran and Iraq. Earlier they were briefly detained in the Iraqi city of Kirkuk but released after receiving assistance from the Russian Embassy, RIA-Novosti said.