Turkey sent helicopter gunships against Kurdish rebels Friday after air strikes on their bases in northern Iraq overnight, while seeking support from its neighbours for its military campaign.
Three days after Kurdish rebels killed 24 soldiers along the Turkish-Iraqi border, the army's biggest losses at their hands since 1993, jets and helicopters kept up their attacks in support of 10,000 troops on the ground.
"While the majority of the land and air operations are in (Turkey), mainly in the Cukurca region, ground and air strikes are ongoing in a few points in northern Iraq across the border," the army said in a statement on its website.
Cukurca, in southeastern Turkey's Hakkari province, is on the border with Iraq.
A small group of specially trained Turkish troops crossed into Iraq, entering the Dola Sulo region in Haftanin, the Kurdish news agency Firatnews quoted sources from the Kurdistan Workers' Party (PKK) as saying Thursday.
Firing and the sound of helicopters could be heard overnight in Cukurca.
The Turkish army on Thursday initiated "a large-scale land operation" with 22 battalions and supported by air strikes against the rebels in five separate spots inside Turkey and across the border, the general staff said.
Interior Minister Idris Naim Sahin described it as one of the biggest operations ever against the PKK in comments to the NTV channel Friday.
Turkish Prime Minister Recep Tayyip Erdogan, heavily criticised by opposition deputies for his handling of the Kurdish conflict, said it was a "complex problem" that was not only a military one.
But he was critical of some European countries, which he did not name, for not doing enough to tackle the PKK presence inside their borders.
Around 10,000 soldiers took part in the operation, Turkish media reported Friday. Some 6,000 of them were special forces, the daily Sabah said.
The battalions include commando units, gendarmerie and special forces, the army said, without specifying how many had entered Iraq.
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Iranian Foreign Minister Ali Akbar Salehi met Friday with his Turkish counterpart Ahmet Davutoglu, saying afterward: "Our first issue to discuss was terrorism. ... The PKK and the Party of Free Life of Kurdistan (PJAK) are the common problem of our countries."
Speaking at a televised joint press conference with Davutoglu, he urged "more serious cooperation" against the rebels.
Davutoglu said: "Our joint determination to fight against PKK and PJAK will go on in its strongest terms."
"From now on we will work together with a joint action plan until this threat of terror is eliminated totally," he said.
Tehran has been carrying out a major offensive against the PJAK, which Turkey considers a branch of the PKK, since July.
Salehi also met with President Abdullah Gul, who earlier said Turkey would exact "huge revenge" against the PKK for the attacks, and was expected to have talks with Erdogan.
Already Thursday, Baghdad had pledged to cooperate with Ankara on security issues.
Nechirvan Barzanil, a former prime minister of the Iraqi Kurdish regional government, offered his support during a surprise visit to Ankara Thursday, when he met Davutoglu and Erdogan.
Tuesday's eight coordinated rebel attacks dealt the worst blow to the army since 1993, when 33 unarmed soldiers were killed in Bitlis province.
Clashes between the PKK and the army have escalated since the summer.
The PKK, listed as a terrorist organisation by Turkey and much of the international community, took up arms in Kurdish-majority southeastern Turkey in 1984, sparking a conflict that has claimed some 45,000 lives.
Turkey's last ground incursion into northern Iraq, an autonomous Kurdish region, was in February 2008, when the army struck against the Zap region.