Fifteen Turkish soldiers were killed in clashes with Kurdish separatist PKK rebels in southeast Turkey, Turkey's general staff said, in one of the deadliest attacks on the military this year.

At least 23 members of the Kurdistan Workers' Party (PKK) were also killed after rebels armed with "heavy weapons" attacked a military outpost in the Semdinli region bordering Iraq and Iran, the military said.

The attack is likely to put pressure on Prime Minister Tayyip Erdogan to strike back at the PKK. Turkey has attacked PKK bases in mountainous northern Iraq several times over the past year, but has confined itself to shelling and air strikes since a brief land offensive in February.

The general staff said two Turkish soldiers were missing and that an operation was under way to rescue them. It said the rebels had received back-up from PKK bases in Iraq.

Erdogan was on an official visit to Turkmenistan yesterday but said he was returning to Turkey for an emergency security meeting.

"The struggle against terrorism will continue with the same determination as before," he told an audience in Ashgabat.

Parliament is this month likely to approve a government request to extend a mandate to launch military operations against the PKK in Iraq as needed. The current mandate expires on 17 October.

Turkey blames the PKK, considered a terrorist organisation by the United States and the European Union, for the deaths of more than 40,000 people since it launched its campaign for an ethnic Kurdish homeland in southeast Turkey in 1984.

Washington is sharing vital intelligence with Turkey on PKK movements in Iraq. The United States and the European Union have expressed concerns that prolonged Turkish military operations inside Iraq could further destabilise Iraq and the wider region.

Friday's attack is the first serious challenge for Turkey's new military chief, General Ilker Basbug, who took over NATO's second-largest army in August.