Three special forces servicemen who were being prosecuted for massacring a group of Chechen civilians in one of Russia's highest profile criminal trials have gone on the run days before proceedings were expected to draw to a close.

The three men in the Ulman case - named after the officer who controlled the GRU (chief military intelligence directorate) unit - had been granted bail despite protests from the victims' families.

Captain Eduard Ulman, Alexander Kalagansky and Vladimir Voyevodin previously admitted shooting six Chechens, including a pregnant woman, on a mountain road in southern Chechnya in January 2002, but claimed they were innocent because they were following orders.

Their prosecution has been seen as a test case for attempts to punish war crimes in Chechnya, although critics have questioned why senior officers have not been prosecuted.

A federal warrant was issued for the men's arrest after they failed to appear for two hearings in the southern city of Rostov-on-Don. Last week prosecutors demanded prison terms of between 18 and 23 years for the soldiers.

Murat Musaev, a lawyer for the victims' families, said the court had repeatedly refused requests to detain the defendants during their prosecution. "We were afraid this would happen," he said. "It was clear that they would be found guilty and of course no one wants to sit in prison for 20 years."

Their escape will be an embarrassment for the Kremlin, which has struggled to persuade critics that it is serious about holding war criminals to account after more than a decade of conflict in Chechnya.

The incident that prompted the trial took place near the Chechen village of Dai when the GRU team mistakenly opened fire on a minibus carrying civilians, killing one and wounding two. The unit was jittery because it was engaged in a sweep designed to capture an Arab warlord, Khattab, fighting on the side of Chechen separatists.

The court heard that after bandaging the wounded Capt Ulman radioed for orders from his superiors, who instructed him to kill the five survivors, apparently in an attempt to cover up the initial blunder. Mr Musaev said: "By running away these men have shown to the whole world that they know they are guilty."