CUKURCA, Turkey (Reuters) - Turkey and Iran pledged on Friday to cooperate in the fight against Kurdish militants, as thousands of Turkish troops pressed ahead with an air and ground offensive for a third day following an attack that killed 24 Turkish soldiers.
The counter-insurgency operation against separatist fighters from the Kurdistan Workers' Party (PKK) was concentrated on both sides of Turkey's border with northern Iraq.
Hundreds of Turkish soldiers were hunting PKK fighters around the Zab river areas a few kilometres inside Iraqi territory, security officials said.
Turkey's reaction to one of the most deadly attacks on its security forces in a conflict that began three decades ago has ignited speculation that Turkey could move to a full blown incursion to clear out PKK camps deeper inside northern Iraq.
The prospect would heighten risks in an already unstable region, with U.S. troops due to withdraw from Iraq this year, and neighboring Syria in the grip of a brutal repression against pro-democracy protesters.
Turkey, Iraq, Syria and Iran all have large ethnic Kurdish minorities, but the separatist struggle is fiercest in NATO member Turkey, where more than 40,000 people have been killed in the violence.
The neighborhood is rife with suspicions over who could be supporting the Kurdish militants.
On Friday, Iran's Foreign Minister Ali Akbar Salehi paid an unscheduled visit to Ankara to assure Turkey of Tehran's support, and to deny reports of suspected Iranian duplicity in the Turkish media.
At a joint news conference with Turkish counterpart, Ahmet Davutoglu, the Iranian minister said Kurdish militants were a common problem and the two countries should deepen cooperation against the PKK, and its Iranian offshoot, the Party of Free Life of Kurdistan, or PJAK.
"PKK and PJAK are common problems for Turkey and Iran, our determination continues, we should fight them with more serious coordination," Salehi said.
The Iranian minister described both the PKK and PJAK as "terrorist groups". The United States, European Union and Turkey have listed the PKK as a terrorist organisation.
"Our common determination in fighting against PKK and PJAK will continue in the strongest way. We will work together in a common action plan until the area is completely free of the threat of terror," Davutoglu said.
It was unclear how Tehran and Ankara would work together. Until their relations soured in the past couple of years, Turkey and Israel had shared intelligence on regional security threats to their countries.
The Qandil mountains, on the Iraq-Iran border, are the main base of the PKK bases. Iranian forces have in the past shelled targets at Qandil.
Turkish Prime Minister Tayyip Erdogan has signalled in the past Turkey could launch a joint operation with Iran against Kurdish militants' in northern Iraq.
The current theatre of operations on the Zab river is further west than the Qandil mountains.
On Friday, the Turkish military said most of the current operations were being carried out on the Turkish side of the border with Iraq.
"The large part of air and ground operations are carried out in the country, focusing mainly on the Cukurca area, and air and ground operations continue in a few areas of northern Iraq," the military said in a statement posted on its website.
The military has said it has put troops from 22 battalions into the field for ground attacks in five different areas on either side of the border, and has also launched air strikes.
A Reuters reporter in Cukurca, one of the districts in the southeast province of Hakkari where the militant attacks by the PKK took place, saw little military activity in the area, apart from warplanes flying at high altitude overhead.
Erdogan is under pressure to show decisive action after the latest killings. A full-blown Turkish military incursion into Iraq may assuage public anger, but would not deal a fatal blow to the rebels and could damage ties with Middle East neighbours.
Ties between Ankara and Tehran have come under strain after Turkey decided to host a radar system for a NATO missile shield programme.
Turkey's increasing criticism of Syrian President Bashar al-Assad's crackdown has also chilled ties.
On Friday, Salehi and Davutoglu said relations between the two countries were in excellent shape.
In the past week, Turkish media has carried reports that Iran had captured the second in command of the PKK, Murat Karayilan, only to release him after Turkish air strikes on the base where the militant commander had been.
Salehi denied those reports.
"Murat Karayilan was never captured by Iranians," Salehi told reporters. "If we had caught him, we would have given him to our Turkish brothers. What interest could Iran have in capturing him and then releasing him? We don't have such a policy."
Additional reporting by Tulay Karadeniz; Writing by Ibon Villelabeitia