Darren Hickey: Exact circumstances of death unknown

They had been staying in the Chechen capital, Grozny, while installing a telecommunication system.

Ruslan Akhmadov, who is accused of ordering their deaths, has been arrested in Azerbaijan and handed over to the Russians with another wanted rebel leader, Badrudi Murtazayev.

The Foreign Office is monitoring the latest developments.

A spokesman said: "We are urgently checking these reports and are in touch with the families. We cannot say anything more and do not have any more information."

An inquest in the UK in October 1999 ruled that the men were unlawfully killed.

Rudulf Petschi: On engineering contract

The victims' severed heads were found by a road in war-torn Chechnya.

The men's bodies were handed over to the British ambassador in neighbouring Azerbaijan in December 1998, before being put on a plane for London.

Although the exact circumstances of the mens' death remains unclear, Westminster Coroners' Court heard that the men had been starved of food and water, and were repeatedly beaten before being decapitated.

Two of the men, both "wasting away", showed evidence of being tied up before they were beaten unconscious and their heads cut off from behind with a large blade, Home Office pathologist Dr Iain West told that hearing.

This is without question a major coup on the part of the Russian law-enforcement agencies

Kremlin aide Sergey Yastrzhembskiy

Three of the engineers were working for Surrey-based Granger Telecom and one worked for British Telecom.

At the time of the men's deaths, Tory MP Angela Browning called for an inquiry into how the Foreign Office handled an investigation into the murders.

The Chechen suspects were arrested in Azerbaijan and extradited to Russia, where they were paraded on Russian television on Sunday.

A Kremlin spokesman said Ruslan Akhmadov was a member of a gang that kidnapped and killed the four telecoms engineers.

The Kremlin's chief spokesman on Chechnya, Sergey Yastrzhembskiy, said: "This is without question a major coup on the part of the Russian law-enforcement agencies".

Mr Akhmadov and the other detainee - Badrudi Murtazayev - were arrested in the Azerbaijani capital Baku on Wednesday. News of their arrest and handover to Russia emerged only on Sunday.

They are now being held in Makhachkala, capital of the Russian republic of Dagestan, which borders on Chechnya.

Russian Public TV said Mr Akhmadov was accused of having a hand in "more than 30 kidnappings - and most likely this is just the tip of the iceberg".