The row further strained US-Turkish relations, already at a low point over Ankara's refusal to back the war in Iraq.

The 11 soldiers from Turkey's special forces were arrested on July 4 in Sulaymaniyah, in Kurdish-held northern Iraq, suspected of plotting to harm Iraqi civilian officials, according to the United States.

The soldiers were released late Sunday following a wave of protests by civilians and complaints by top Turkish government officials to the US administration.

"Unfortunately, this incident has led to the biggest crisis of confidence between Turkish and US forces, and has turned into a crisis," Hilmi Ozkok told reporters as he received the US ambassador to Ankara, Robert Pearson, who is leaving Turkey at the end of his term.

Ozkok said he believed the arrest of the soldiers was not the result of a "US army policy", but expressed doubt that it was merely a local US officer who had carried out the arrests on his own.

"Considering the senior status of the people we contacted and the amount of the time before the soldiers' release, I find it difficult to evaluate this merely as a local incident," he said.

Turkey greatly angered the United States when its parliament refused in March to allow US troops to use its territory to invade neighbouring Iraq from the north.

Ankara's bid to bolster its military presence in northern Iraq -- where it feared local Kurds would declare an independent state -- during the war also strained transatlantic ties.

Government spokesman Cemil Cicek said the latest incident justified Turkey's concerns over northern Iraq, adding that Turkish troops would stay in the area.

"There has so far been no demand for our troops to leave the region. It is obvious why our soldiers are there... There is still a power vacuum in Iraq," Cicek told reporters after a cabinet meeting.

US Vice President Dick Cheney, meanwhile, phoned Turkish Prime Minister Recep Tayyip Erdogan Monday to say that the US would work to clarify the incident, a statement from Erdogan's office said.

Turkish and US officials are to jointly investigate the incident.

Erdogan, for his part, demanded that those responsible for causing "unnecessary tension" in bilateral relations be sanctioned, the statement said.

US officials said the troops were detained along with other suspects on "suspicion of involvement in an alleged plot to harm Iraqi civilian officials in northern Iraq."

Turkish media reports have suggested that the Turkish troops were arrested because of a tip-off relating to a possible plot to assassinate the Kurdish governor of Kirkuk.

"I do not know what the intelligence was, but it is totally unacceptable that intelligence be investigated in this manner," Ozkok said.

"We accord importance to Turkish-US ties and relations between the US and Turkish armies... but another thing just as important as these ties is our national honour and the honour of the Turkish armed forces," he said.

The Turkish army has already made its displeasure known -- it has withdrawn two high ranking officers serving with US Central Command in Tampa, Florida, and a top general cancelled a visit to Tampa to attend a handover ceremony.

The Turkish press warned that the incident will greatly undermine bilateral ties.

"By acting this way, the US has lost even its best friends in Turkey," an editorial in the mass-circulation Hurriyet said. "It will not be easy in the least to erase the marks of this incident."

The liberal Radikal daily said the row could spell the "definite end" to the strategic partnership between Ankara and Washington.

"What is logical is to give up on the desire to re-establish the strategic partnership and find ways to stay friends. There is an urgent need to redefine Turkish-US ties," it said.

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