"The government should put in place a plan on the progressive withdrawal of its troops in Iraq with a view to the last battalion leaving at the end of January 2005 at the latest," the motion read.

Bulgaria has 470 soldiers stationed in Iraq as part of international force under Polish command, and pressure has mounted on the government to withdraw its men following a deadly suicide bombing in December and the kidnapping of two Bulgarian civilians this month.

The government has maintained that it will keep its military contingent in post-war Iraq "for as long as the Iraqis wish" or until the end of 2005, in accordance with a UN resolution.

UN resolution 1546, adopted in June, foresees free elections in Iraq by January 31, 2005 at the latest and the formation of a democratic government by the end of that year.

It adds that the mandate of international forces in the country will expire once this political process has been completed.

The Socialists' motion comes after an Islamist website on Wednesday published a photograph of a severed head which it identified as that of one of the Bulgarian truck drivers who were taken hostage by a group linked to Al-Qaeda.

Bulgarian foreign ministry spokeswoman Guergana Grantcharova said the authorities were trying to verify the authenticity of the claim, but added that the picture was "of very poor quality and therefore reaching any conclusion was difficult."

It shows a hooded man holding a head by its hair in front of a black flag with the emblem of the Tawhid wa al-Jihad (Unification and Holy War) group of alleged Al-Qaeda operative Abu Mussab al-Zarqawi.

The militant group claimed responsibility for the kidnapping on July 8 of Georgy Lazov, 30, and Ivailo Kepov, 32, near the northern Iraqi town of Mosul.

The Arab television station Al-Jazeera reported on July 13 that one of the men had been decapitated by the group, and showed footage of the man just before he was executed.

On July 22, the Bulgarian government identified a body found in the Tigris river as that of Lazov.

Kepov's fate remains unknown, but the government has warned that it is unlikely he is still alive.

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