Turkey and Iran have vowed to collaborate in their fight against Kurdish fighters, as thousands of Turkish troops resumed their air and ground offensive against the armed groups in northern Iraq for a second day.

The foreign ministers of the two countries announced plans to co-operate against the Kurdistan Workers' Party (PKK) and its Iranian wing, the Party of Free Life of Kurdistan (PJAK) during a joint news conference held in Ankara on Friday.

"From now on, we will work together in a joint action plan until this terrorist threat is totally eliminated," Ahmet Davutoglu, the Turkish foreign minister, said.

Ali Akbar Salehi, the Iranian foreign minister, said he will seek more co-operation with Turkey against the fighters near their shared border. He said the PKK and PJAK were "common problems" for both countries.

Davutoglu’s statement came as Turkish jets kept up bombing raids on Kurdish fighter bases, taking off from Diyarbakir, the regional capital of the mainly Kurdish southeast.

The Turkish army has said that "while the majority of the land and air operations are in the Cukurca region [in Turkey], ground and air strikes are ongoing in a few points in northern Iraq across the border".

A small group of specially trained Turkish troops crossed into Iraq from the villages of Yekmal and Bilecan on the Turkish side of the border and entered the Dola Sulo region in Haftanin, the Kurdish news agency Firatnews quoted sources from the PKK as saying.

Attacks 'avoidable'

In the meeting with Davutoglu, Salehi said that the deaths of Turkish soldiers might have been avoided if the US had informed Turkey that the fighters were infiltrating into the country with heavy weaponry.

The US shares intelligence from surveillance drones with Turkey about movement of Kurdish rebels along the border.

Tehran has been carrying out a major offensive against PJAK since July, which Turkey considers a branch of the PKK.

Both armed groups, labeled as terrorist organisations by much of the international community, have been fighting for Kurdish autonomy in their respective countries.

On Thursday, the Turkish army initiated "a large-scale land operation" with 22 battalions against the fighters in five separate spots inside and across the border, according to the general staff.

Around 10,000 soldiers took part in the operation that began in reaction to the killing of 24 Turkish soldiers by the armed group. Around 6,000 of them were Special Forces, the Turkish daily Sabah said.

Meanwhile, Nechirvan Barzani, a former prime minister of the Kurdish regional government, who paid a surprise visit to Ankara on Thursday, said after meeting with the Turkish foreign minister: "We strongly condemn this attack."

The PKK took up arms in Kurdish-majority southeastern Turkey in 1984, sparking a conflict that has claimed about 45,000 lives.