A car bomb on Sunday struck the Turkish city of Gaziantep, a major refugee hub near the Syrian border, killing at least two policemen and wounding 22 other people as the country reels from a succession of militant attacks.

A car bomb on Sunday struck the Turkish city of Gaziantep, a major refugee hub near the Syrian border, killing at least two policemen and wounding 22 other people as the country reels from a succession of militant attacks.

On a day of violence dubbed "Black Sunday" by the press, three Turkish soldiers died in a separate attack in the province of Mardin to the east, in an ambush by Kurdish militants who have killed hundreds of security forces in a renewed insurgency since last year.

With Turkey on high alert for May Day celebrations, four suspected terrorists were detained in Ankara on suspicion of planning attacks and other May 1 events were cancelled elsewhere over security fears.

One policeman was killed when the car bomb went off outside the police headquarters in Gaziantep and 23 people were wounded, including 19 police, the office of Gaziantep regional governor Ali Yerlikaya said in a statement

One more policeman later died of his wounds in hospital. The governor's office statement did not say which group could be to blame.

Three Turkish soldiers were killed and 14 others wounded in an attack Sunday in the Kurdish-dominated southeast blamed on militants from the outlawed Kurdistan Workers Party (PKK), the army said.

The attack took place in the Nusaybin district of Mardin province, where the army has been conducting a military operation backed by a curfew against the PKK, it said. The Dogan news agency said the PKK opened fire with rockets on an army bomb disposal team.

Turkish police on Sunday detained over 200 people in a crackdown on unauthorized protests during a tense May Day in Istanbul, using tear gas and water can