Turkey's NTV reported that 10,000 troops have moved 10 kilometers (six miles) into Iraq. Thousands more troops are stationed at the border, ready to join the operation.
"The transborder land operation started at 7 p.m. local time [5 p.m. GMT] on Thursday by the Ground Forces with support from the Air Force," the General Staff of the Turkish Armed Forces said in a statement.
It said the operation is only aimed against the terrorist PKK group, not against "the territorial unity and stability of Iraq," stressing that Turkish army units "will return to their permanent basing areas as soon as the set objectives have been attained."
According to the Hurriyet daily, on Thursday military helicopters combed the area and two Turkish warplanes were seen flying toward northern Iraq, but it was not clear whether they were on a bombing mission. Turkey has confirmed a total of five aerial attacks inside Iraq since Dec. 16 against the rebels.
Turkey had said it may launch a major operation against Kurdish insurgents based in northern Iraq in the second half of March.
Turkish Foreign Minister Ali Babacan indicated on Wednesday that weather conditions would be a key factor in a possible operation. However, some military experts suggest that a large-scale land operation, even in the absence of harsh winter conditions, would not be effective.
The Turkish parliament gave the government a mandate last October to conduct cross-border operations in northern Iraq against PKK militants based there. Since mid-December, Turkey has carried out five air raids in the cross-border region, killing at least 175 separatists. According to Turkish General Staff data, there are some 3,500 insurgents in northern Iraq.
Ankara earlier warned about the possibility of moving into northern Iraq to conduct a military operation against PKK militants. Over 40,000 people have been killed in Turkey since 1984, when the PKK started its fight for an ethnic Kurdish state in the southeast of the country.
Since the 2003 U.S.-led overthrow of Saddam Hussein, Turkish separatist Kurds have received increasing, if unacknowledged, support from those living in the three neighboring provinces of oil-rich northern Iraq, whose population has sought autonomy from Baghdad and where local Peshmerga militia formally took over security functions from U.S. forces earlier this month.
Ethnic Kurds have also been actively driving for autonomy in eastern parts of Syria. The borders between the three countries are still unsecured.
The PKK, listed by the U.S., NATO and the EU as a terrorist organization, has been fighting for autonomy status in southeast Turkey for nearly 25 years. The conflict has so far claimed about 40,000 lives.
Turkish authorities have consistently refused to enter into a dialogue with the separatists.
