Turkey's military said Sunday that one of its helicopters went down on the Turkish-Iraqi border and that eight more soldiers were killed in combat during its cross-border ground operation in northern Iraq.
It was not clear if the eight were on board the helicopter.
Kurdish rebels said earlier that they shot down a Turkish military helicopter near the Turkish border.
The new deaths bring the announced Turkish military toll to 15.
Baghdad and Washington fear the conflict between Turkish forces and Kurdish rebels could further destabilize Iraq.
Ankara launched the major cross-border land offensive on Thursday after months of aerial bombardment of PKK targets in the remote, mountainous region. It accuses the rebels of using northern Iraq as a base to stage deadly attacks inside Turkey.
"At 6 p.m. (11 a.m. ET) yesterday, our fighters shot down a Cobra helicopter," Ahmed Danees, head of foreign relations for the separatist Kurdistan Workers Party (PKK), told Reuters in Baghdad by telephone.
He gave no details of casualties but said more information would be released later. The incident occurred during fighting in the remote Chamsku area close to the border, Danees said.
It is virtually impossible to verify the claims of either side because the fighting is taking place in largely inaccessible terrain in tough winter conditions.
U.S. concerns
Early on Sunday Turkish troops patrolled the south of Sirnak province below the snow-topped mountains which border Iraq.
Foot soldiers used metal detectors to search the sides of the remote roads where PKK guerrillas frequently lay mines targeting military vehicles.
A senior Turkish military source told Reuters two brigades made up of around 8,000 troops were taking part. Turkish media have put the number of troops at 10,000, but a senior officer with U.S.-led forces in Baghdad said the number was under 1,000.
Washington is sharing intelligence with NATO ally Turkey on PKK movements in Iraq. It has urged Ankara to limit the campaign to precise rebel targets and to bring it to a swift conclusion.
The United States and the European Union fear a prolonged military campaign inside Iraq would raise the risk of serious clashes between Turkish and Iraqi Kurdish forces and also undermine the fragile U.S.-backed government in Baghdad.
Baghdad has urged Ankara to respect its sovereignty. The autonomous Iraqi Kurdish administration of northern Iraq has vowed a tough response if civilians come under attack.
Isolate PKK?
U.S. Defense Secretary Robert Gates said on Sunday Turkey's campaign would not solve its problems with the rebels and urged Ankara to take political and economic steps to isolate the PKK.
Gates also said Turkey should improve communication with Baghdad about the operation and other efforts against the PKK.
Tehran said on Sunday that in the wake of the Turkish action Iran had reinforced its own borders with Iraq, from where Kurdish rebels allied to the PKK have operated against Iran.
Separately, the pro-PKK Firat news agency, which is based in Europe, quoted a top PKK commander in Iraq as urging Kurds in Turkish cities to join the fight against the Turkish state.
"In the big cities, Kurdish youth must give their reply to the military operations. Kurdistan's guerrillas are not just 7,000 or 10,000, they number hundreds of thousands. They are everywhere... in all Turkish cities," Bahoz Erdal said.
Turkey's impoverished, mainly Kurdish southeast has often seen violent pro-PKK protests, though the region has remained largely peaceful since the start of the ground campaign.
Ankara blames the PKK for the deaths of nearly 40,000 people since the group launched its armed struggle in 1984 for an ethnic homeland in southeast Turkey. Turkey, the United States and European Union classify the PKK as a terrorist organization.
Previous Turkish military operations across the border into northern Iraq in the 1990s failed to wipe out the elusive and highly mobile guerrillas.