Turkey has defended military raids into Iraq, saying it had inflicted "heavy losses" on Kurdish rebels.
Turkish forces are concentrated on the Iraqi border
The Turkish army said its troops had penetrated several kilometres into Iraq on Tuesday, to attack a group trying to infiltrate Turkey.
The raid came two days after Turkey used air strikes for the first time to target alleged PKK rebel positions deeper inside Iraqi territory.
Turkey's prime minister pledged to continue action against the rebels.
"A small-scale operation conducted by ground troops as part of hot pursuit... dealt a heavy blow," the Turkish military said in a statement on its website.
It did not say how many troops were involved.
Kurdish officials in Iraq said at least 300 Turkish troops had crossed the border for 15 hours.
Turkish Prime Minister Recep Tayyip Erdogan said his government would continue to do "whatever is necessary" to counter Kurdish rebels.
In Washington, White House press secretary Dana Perino refused to comment on Tuesday's operation until details of the raid were made clear.
MOUNTING BORDER TENSION
7 Oct PKK rebels kill 13 Turkish troops near Iraqi border
17 Oct - Turkish MPs allow military operations in Iraq
21 Oct - 12 Turkish troops die in PKK ambush near Iraqi border
30 Nov - Turkish cabinet backs PKK pursuits in Iraq
13 Nov - Turkey shells PKK targets in Iraq, Baghdad says
1 Dec - Turkish army targets rebels in Iraq, inflicting "heavy losses"
16 Dec - Turkish jets bomb PKK targets in Iraq for the first time
"Of course we are co-ordinating with the Turkish and Iraqi authorities in the area," Ms Perino said.
"The PKK is a threat to Turkey, to Iraq and to the United States. And so we continue to share information, share intelligence."
But the Associated Press news agency said US officials were only informed about the raids once they were under way and were angered at not being told about the operation in advance.
The US agreed to provide Turkey with intelligence last month in an effort to avert a major Turkish incursion into Iraq.
Iraqi Foreign Minister Hoshyar Zebari, who is a member of the Kurdish Democratic Party (KDP), expressed concern that "unilateral actions" could harm Iraqi and Turkish interests.
But he noted that the recent Turkish raids had been in sparsely populated areas.
"At the same time we fully understand the legitimate concern Turkey has over the PKK terrorist activities against them," he said.
The head of Iraq's Kurdish regional government cancelled a meeting with US Secretary of State Condoleezza Rice in protest at what he said was Washington's tolerance of Turkish raids.
Tuesday's incursion was believed to be the first major Turkish troop deployment in Iraq since Turkey's parliament voted in October to allow the military to launch cross-border operations.
Iraqi officials have said the Turkish air strikes on Sunday targeted 10 villages and killed one woman. The PKK has reported seven deaths.
The Turkish military said "many facilities harbouring the PKK were hit" during the strikes.
"What is true is that the PKK has suffered heavy losses in terms of its infrastructure and its human resources," the statement added.
It denied reports of civilian casualties and of the targeting of civilian areas.
Turkey accuses the PKK of using bases inside Iraq to launch attacks on Turkey.
As many as 3,000 PKK members are believed to be based inside northern Iraq. Turkey has accused the local Kurdish authorities of supporting them.
The UN has said that almost 2,000 people in northern Iraq have been forced to flee their homes in recent days because of Turkish raids.