A Russian military convoy has been attacked by rebels in its volatile southern region of Ingushetia, reported BBC.
Official Russian reports of the ambush, which has been blamed on local Muslim separatists, said two soldiers were killed and several more were injured.
But Ingushetian opposition reports suggested as many as 40 Russian soldiers were killed.
The convoy came under grenade attack and machine gun fire near Nazran, capital of the north Caucasus region.
"A search of the area is currently taking place, the bandits who carried out the attack on a defence ministry military column are being tracked," said a Russian official, quoted by Interfax news agency.
Russian news agencies reported that one armoured personnel carrier and two lorries had been damaged in the incident.
However, an Ingushetian law enforcement source quoted by Reuters said 40 soldiers were killed in the ambush.
The source said three armoured personnel carriers and two lorries were hit, and all but one of the soldiers in the convoy were killed.
If confirmed this would be the worst loss for the Russian military in a series of recent attacks on troops in Ingushetia.
The territory borders on Chechnya, where Russian forces have engaged in heavy fighting with separatist rebels in recent years.
The Ingush authorities say they are fighting a war against terrorism, and blame Islamist militants for the attacks.
Last month the Moscow Helsinki Group, a human rights organisation, said "state-sponsored terror" in Ingushetia could plunge the country into civil war.