It’s the first confirmed ground operation by the Turkish military into Iraq since the US-led invasion that toppled Saddam Hussein. It has raised concerns that it could trigger a wider conflict with the US-backed Iraqi Kurds.

The ground operation started after Turkish warplanes and artillery bombed suspected rebel targets on Thursday, the military said on its web site. The ground incursion was backed by the Air Force, the statement said. Turkey has conducted air raids against the PKK guerrillas in northern Iraq since December, with the help of US intelligence, and it has periodically carried out so-called “hot pursuits” in which small units sometimes spend only a few hours inside Iraq.

So the announcement of a cross-border, ground incursion of a type that Turkey carried out before the US-led invasion of Iraq in 2003 was a major development in the conflict.

“The Turkish Armed Forces, which values Iraq’s territorial integrity and its stability, will return as soon as planned goals are achieved,” the military 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 offensive and had penetrated six miles into 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.

The military said its target was the PKK and that it would take care not to harm civilians and other local groups that do not act in enmity against the Turkish Armed Forces.

Nihat Ali Ozcan, a terrorism expert with the research centre 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.

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. Fouad Hussein, a spokesman for the semi-autonomous Kurdish government, said the Kurdish Peshmerga forces had been put on alert.