The United States has urged Turkey to bring current military operations in Iraq to a swift conclusion, the Pentagon said on Friday.
"We have strongly urged the Turkish government to bring any ongoing operations to a swift conclusion," Pentagon spokesman Bryan Whitman told reporters.
Turkish troops launched a ground incursion across the border in pursuit of Kurdish rebels earlier on Friday.
The ground operation started after Turkish warplanes and artillery bombed suspected rebel targets on Thursday, the military said on its Web site. "After the successful bombing, a cross-border ground incursion backed by the Air Force started at 1900 (1700 GMT)" on Thursday, it said.
"The Turkish Armed Forces, which values Iraq's territorial integrity and its stability, will return as soon as planned goals are achieved," the statement said. "The executed operation will prevent the region from being a permanent and safe base for the terrorists and will contribute to Iraq's stability and internal peace."
Private NTV television said 10,000 troops were taking part in the cross-border offensive, which follows periodic air raids on suspected hideouts of the PKK rebel group in Iraq. The Kurdish militants are fighting for autonomy in Turkey's predominantly Kurdish southeast, and have carried out attacks on Turkish targets from bases in northern Iraq.
Nihat Ali Ozcan, a terrorism expert with the research center TEPAV, said the operation was launched at this time to hit the group before any infiltration by rebels into Turkey in the spring, the traditional start of the fighting season.
"I think it is aimed to keep the PKK under pressure before the group starts entering Turkey," he said on CNN-Turk television. "I don't think the operation is a large-scale one."
An Iraqi border forces officer, Col. Hussein Tamer, said Turkish shelling on Thursday hit several Kurdish villages in the Sedafan area, some 20 miles from the border.
Jabbar Yawar, a spokesman for Iraqi Kurdish security forces, said sporadic bombing was taking place in the border areas, but no casualties were reported.
Kurdish Peshmerga forces on alert
Fouad Hussein, a spokesman for the semiautonomous Kurdish government, said the Kurdish Peshmerga forces had been put on alert. He said Iraqi Kurdish forces also had tightened security around bases housing Turkish military monitors operating in northern Iraq with permission from local authorities under a 1996 agreement.
"The government of Kurdistan ordered the Peshmerga forces to be on alert in fear of any Turkish incursion on Iraqi territory," he said, claiming that Turkish military monitors had tried to leave their bases in violation of the terms of the 1996 agreement.
"Those troops tried to move out but the Peshmerga forces forced them to return to their camps within half an hour," he said.
In Ankara on Thursday, Turkey's civilian and military leaders issued a statement after a meeting on national security, saying cross-border attacks by the military would continue as long they were "deemed necessary."
Turkey has staged ground incursions against Turkish Kurd rebels in northern Iraq in past years. The PKK launched its guerrilla campaign in 1984, and as many as 40,000 people have died.