"My government is appalled by the recent attack," said Matthew Bryza, the deputy assistant secretary of state for European and Eurasian affairs.

"We are doing what we can, working with the Turkish government and the Iraqi government to make sure that the remaining hostages are freed," he said.

Bryza was speaking at a meeting here of foreign ministers of the Organisation of Black Sea Economic Cooperation (BSEC).

He reiterated Washington's commitment to help Turkey combat the separatist Kurdistan Workers' Party (PKK), whose bases in northern Iraq have prompted Turkish threats of a military incursion, despite strong US objections.

"We've made a whole series of commitments on eliminating the PKK terrorist threat. We mean it. We'll deliver on those promises. We are working on it... with the Turkish government and the Iraqi government," Bryza said.

"We know we need to produce concrete results," he added.

The PKK has pledged it will not harm the soldiers it said it captured during an ambush on a military unit near the Iraqi border on Sunday.

The group on Tuesday released what it said were photographs of the captives.

The Turkish army has confirmed that eight soldiers are missing.

The ambush incresed pressure on the government to take military action in northern Iraq where the rebels, Ankara says, are tolerated and even supported by the local Iraqi Kurdish leadership.

Turkish leaders say they will follow through with their threat if Washington and Baghdad fail to end the safe haven that the PKK, listed as a terrorist organisation by Ankara and much of the international community, enjoys there.