The heads of three Britons and a New Zealander were found in a sack on a road west of the Chechen capital, Grozny, on 8 December.

Police say the four were killed after a rescue attempt went wrong.

Darren Hickey, 26, Peter Kennedy, 46, and 42-year-old Rudi Petschi, and New Zealander Stan Shaw, 58, were killed as Chechen special forces closed in on their kidnappers.

The had been abducted on 3 October in Grozny, where they were installing a cellular phone system.

Prisoner release demanded

Chechen leaders had promised to deliver the heads to the British and New Zealand embassies in Moscow on Tuesday.

All four victims worked for Granger Telecom

The Chechen Prosecutor-General, Mansur Tagirov, said there was also a "well-justified hope" that the victims' headless bodies could also be recovered within the next few days.

He is reported to have said that the people in possession of the corpses had been contacted, but were demanding the release of one of their jailed comrades before giving up the remains.

According to Russian reports - denied in Grozny - the Chechen gang behind the executions has issued a $2,000 ransom demand for the return of each body.

Law and order have disintegrated in Chechnya since the end of a bloody war of independence with Russia two years ago.