Army chief Yasar Buyukanit on Thursday became the first such high-ranking military official to publicly argue for a cross-border operation and ask for government permission to send troops to crack down on bases of the outlawed Kurdistan Workers' Party (PKK) in northern Iraq.

"If you ask me whether a cross-border operation is needed, yes it is needed. It would be useful," Buyukanit told a press conference here.

Indignation is Turkey is growing over Iraqi and US failure to fulfill pledges to eradicate the PKK and recent Iraqi Kurdish threats, said Serhat Erkman, an expert on the Middle East at the Ankara-based think-tank ASAM.

"As a result, Turkish leaders have begun to stress more openly the need to implement economic, political and 'other' measures, besides diplomacy, to resolve the issue," he said.

Turkey charges that several thousand PKK rebels have found refuge in northern Iraq where they enjoy unrestricted movement and obtain weapons and explosives for attacks on Turkish targets in their 22-year struggle for self-rule in southeastern Turkey.

Ten Turkish soldiers and 29 rebels were killed this month -- in the heaviest fighting between the PKK and the army in a long time -- as the arrival of spring makes the mountainous crossing between Iraq and Turkey more accessible to the rebels.

Ankara accuses Iraqi Kurds of tolerating and even supporting the rebels.

Tensions between the two sides rose this week after Massud Barzani, the head of the autonomous Kurdish region in northern Iraq, threatened to fan unrest in Turkey's Kurdish-populated southeast if Ankara continues to oppose Kurdish claims on the oil-rich ethnically volatile Iraqi city of Kirkuk.

Turkey claims that thousands of Kurds have moved into Kirkuk to change its demography ahead of a referendum on Kirkuk's future status, scheduled for the end of the year, and has called for the postponement of the vote.

Ankara worries that Kurdish control of Kirkuk and its vast oil reserves would embolden what it believes are Kurdish ambitions to break away from Baghdad -- a prospect it fears could set up an example for Kurds in adjoining southeast Turkey.

At Thursday's press conference, Buyukanit described Barzani's words as unacceptable and implicitly accused the United States of emboldening the Iraqi Kurdish leader. "We all know who has spoilt (Barzani)," the general said.

"This was the first time in Turkish history that an army chief has challenged the United States without giving names," said Sedat Laciner, the head of the Ankara-based think-tank USAK.

"Turkey has long waited for the United States to do something about PKK rebels, but Barzani's remarks were the last straw," he added. "We are gradually moving towards a military incursion. Turkey is not bluffing."

Washington opposes a possible Turkish incursion into northern Iraq, which it fears would destabilise the relatively calm area, and has instead argued for non-military means.

"Certainly that's an option that everybody should work to avoid," State Department spokesman Sean McCormack said Thursday in response to Buyukanit's remarks.

Dogu Ergil, a professor of political science at Ankara University, described Washington's stance as an argument that no longer convinces Ankara.

"It is a great contradiction that the United States, which has invaded Iraq, tells Turkey that a military option is not such a good idea," Ergil said.

There is a high possibility that Turkey could engage in a cross-border operation after presidential elections in May, he added.

"Buyukanit has clearly underlined that Turkey is ready to launch a large-scale operation in Iraq, no matter what the United States or Iraqi Kurds say," he said.