Russia's armed forces have launched a counter-terrorist operation in the Caucasus region of Ingushetia after an attack on a convoy of Interior Ministry troops.

State-controlled Russian news agencies reported that two soldiers had died but a regional law enforcement source said 40 were killed in the attack, making it the most deadly in a recent series of attacks on troops in Ingushetia, a small territory bordering Chechnya.

"The soldiers didn't even manage to resist, because several rocket-propelled grenades hit their trucks," the source said, adding that three armoured personnel carriers and two trucks were hit by automatic rifle fire and grenades.

All but one soldier travelling in the convoy were killed, the source said.

News agencies quoted a spokesman for the region's Interior Ministry as saying two soldiers had been killed and five wounded. The agencies reported that one armoured personnel carrier and two trucks had been damaged in the shooting.

RIA Novosti quoted the regional prosecutor, Yuri Turygin, as saying the attack was carried out by as many as 20 fighters from Chechnya and Ingushetia.

A spokesman for the Ingushetian Interior Ministry said earlier that a convoy came under fire near the village of Muzhichi, about 25km east of the regional capital Nazran, but was unable to confirm casualties.

Troops were checking vehicles at the border with Chechnya.

A Muzhichi resident, reached by telephone, said troops had barricaded the village and were checking passports while two helicopters circled overhead.

An opposition website, which moved from ingushetiya.ru to ingushetia.org several weeks after its former owner, Magomed Yevloyev, was shot in the head while in police custody, said the toll was higher and troops were killed in two separate attacks.

Around 50 soldiers were killed in the first attack, while one survived with serious head wounds, the website said. Two more were killed when another convoy, sent to reinforce the first, came under attack, it said.

- Reuters