Undersecretary of State Nicholas Burns said after talks with Prime Minister Recep Tayyip Erdogan that Washington would continue to support Ankara's struggle against the separatist Kurdistan Workers' Party (PKK), listed as a terrorist group by both countries.

Referring to a search conducted Wednesday by Iraqi and US forces at the Mahmour refugee camp in northern Iraq, which Ankara says is under PKK control, Burns said he hoped it was "the beginning of a serious effort to close the camp and make sure that northern Iraq is not used by the PKK to attack in Turkey."

Ankara says Kurdish-run northern Iraq has become a training ground for the PKK, where the rebels enjoy unrestricted movement and are easily able to obtain weapons and explosives.

Earlier this month, Erdogan accused Washington and Baghdad of failing to keep promises to curb the rebels and asked whether the appointment of a US envoy to coordinate joint efforts against the PKK in August was "a tactic" to distract Turkey.

Ankara has threatened a cross-border military operation to crack down on the PKK if Washington and Iraqi forces fail to take measures.

Burns sounded less supporting on another Turkish concern regarding Iraq -- the future of the ethnically mixed oil-rich city of Kirkuk, which the Iraqi Kurds want to incorporate into their autonomous region in northern Iraq.

"We understand the importance of this issue, we understand how sensitive it is," he said.

"We'll be very pleased to listen to the Turkish authorities but it's gonna be most important for the Iraqi authorities to deal with this question in the first place," he added.

Kirkuk has a significant population of Turkmen, a community of Turkish descent backed by Ankara.

Turkey accuses the Iraqi Kurds of having moved thousands of their people to Kirkuk and its environs since the US-led invasion in 2003 in a bid to change its demographic structure in their favour ahead of a referendum on the city's status, planned for 2007.

Ankara fears that Kurdish control of Kirkuk and its oil reserves will boost what it sees as Kurdish ambitions to break away from Baghdad, a scenario that is likely to fan separatism among its own Kurds in adjoining southeast Turkey.

Burns was in Ankara on the first leg of a regional tour, the latest in a string of top-level US officials sent to sell President George W. Bush's new Iraq plan to anxious allies.

He was scheduled to meet Foreign Minister Abdullah Gul and military officials Friday.