Four suspects have been detained in connection with the attack, Interior Minister Idris Naim Sahin told reporters.

Two militants set off a bomb inside their car near a police station at Pinarbasi in Turkey's central Kayseri province on Friday, killing themselves and one policeman and wounding 18 others.

A statement on a PKK website said Pinarbasi was the intended target and the bombing was a response to Turkish military attacks, rejecting Turkish media reports that the actual target was in the capital Ankara.

"We have seized four people. Their foreign links have been revealed," Sahin said.

He did not elaborate but broadcaster NTV reported security sources as saying the bombers entered Turkey from neighbouring Syria which is in the grip of a the 14-month-old revolt against President Bashar al-Assad.

The Syrian border region is not generally an area of major PKK activity but this month, three Turkish soldiers were killed in clashes with the rebels near the border, a region which has seen thousands of refugees fleeing from the Syrian conflict.

The PKK threatened in March to step up attacks in Turkey if its forces entered Syria after Prime Minister Tayyip Erdogan, one of Assad's most vocal critics, mooted the possibility of establishing buffer zones within Syria to protect civilians.

The PKK threat signalled a possible renewed alliance with Damascus, which backed the rebels in the 1980s and 1990s.

Sahin said on Friday police followed the car from Goksun district in Kahramanmaras to Pinarbasi, about 100 km (60 miles), after it passed a checkpoint in the road without stopping.

Police opened fire as it passed the Pinarbasi police station and the bomb was detonated. Pinarbasi is east of Kayseri city, some 325 km (200 miles) southeast of the capital Ankara.

More than 40,000 people have been killed in the PKK insurgency since the group took up arms against the state in 1984. The PKK is listed as a terrorist organisation by Turkey, the United States and the European Union.