Ankara began probing the issue this month after a militant of the Kurdistan Workers' Party (PKK) who surrendered to the Turkish authorities said he once saw two US armoured vehicles deliver weapons to a PKK camp in Iraq's Qandil mountains, on the border with Iran.

The Turkish army "also have suspicions, they have certain documents," Gul said in remarks published in the Radikal newspaper.

"We called the US ambassador to the foreign ministry. My undersecretary showed him the documents... He said this could not be possible, but said he would ask Washington to look into the issue," Gul said.

The minister said he also raised the issue in a telephone conversation with US Secretary of State Condoleezza Rice last week.

Ankara says its patience is running out over the safe haven that PKK rebels enjoy in Kurdish-run northern Iraq, despite the fact that the United States, a NATO ally, also lists the group as a terrorist organisation.

Turkey has accused Iraqi Kurds of tolerating and even aiding the rebels, who, it says, obtain weapons and explosives in the region for attacks across the border.

Prime Minister Recep Tayyip Erdogan is under pressure to order a military operation into northern Iraq after the PKK notably stepped up attacks inside Turkey this year. The army has amassed troops at the Iraqi border.

Turkey's envoy to the United States said Wednesday the forces of Massud Barzani, head of the autonomous Kurdish region in northern Iraq, provided the PKK not only with safe haven "but also logistical support -- food and other means, weapons, ammunitions, explosives."

"We know the United States is supplying arms to the northern Iraqi administration, and it is just possible that they are ending up in the hands of the terrorist organisations," Ambassador Nabi Sensoy said in Washington.

The United States has warned Turkey against a cross-border operation, wary that such a move may destabilise a relatively peaceful region in conflict-torn Iraq and fuel tensions between Ankara and the Iraqi Kurds, a staunch US ally.

Washington says it is working to curb the PKK through non-military means such as cutting off its financial resources.

The PKK took up arms for Kurdish self-rule in southeast Turkey in 1984. The conflict has claimed more than 37,000 lives.