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 people as the country reels from a succession of militant attacks.
On a day of violence dubbed "Black Sunday" by local media, 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 jihadists 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 police officer later died of his wounds in hospital. The governor's office statement did not say which group could be to blame.
- 'Link to IS jihadists' -
Turkish news reports said the investigation was focusing on the possibility the attack was carried out by Islamic State (IS) jihadists who still control territory in Syria on the other side of the border.
Police arrested the father of a known IS member in the city, named as Ismail G., and were carrying out DNA tests to ascertain if the son was the perpetrator, the Hurriyet daily said.
One of the main cities of Turkey's southeast, Gaziantep has a population of around 1.5 million and is an important centre for refugees who have fled the war in neighbouring Syria.
The bombing comes with Turkey on edge after two deadly attacks in Istanbul this year blamed on IS jihadists and a pair of attacks in Ankara that were claimed by Kurdish militants and killed dozens.
The latest attack in the heart of one of the country's main urban centres is likely to further raise alarm about security in Turkey, which has seen tourism fall sharply since the start of the year.
A top flight Turkish basketball league match between Fenerbahce of Istanbul and Gaziantep due to be played in the city Sunday afternoon was postponed after the attack.
- Three soldiers killed by PKK -
Signup to our newsletter and follow us on Facebook and Twitter!
eanwhile three Turkish soldiers were killed and 14 others wounded in the attack in Kurdish-dominated Mardin province to the east of Gaziantep carried out by Kurdistan Workers Party (PKK) militants, the army said.
The attack took place in the Nusaybin district of Mardin, 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.
The PKK -- which has fought an insurgency against the Turkish state for more than three decades -- has killed hundreds of members of the security forces in the southeast since a truce collapsed last summer.
With Turkey on edge, a female suicide bomber on Wednesday blew herself up in the usually peaceful former Ottoman capital of Bursa, south of Istanbul.
The Kurdistan Freedom Falcons (TAK) -- a radical splinter group of the better-known PKK -- on Sunday claimed the Bursa attack, saying the female suicide bomber had detonated her charge before reaching the intended target.
- New IS rocket strike on Kilis -
Also on Sunday, four people were wounded in the Turkish town of Kilis, just south of Gaziantep, by rockets fired from an IS-controlled area of Syria, Anatolia said.
Eighteen people, including Syrian refugees, have been killed in Kilis by IS rocket attacks since January, prompting anxiety and anger among local residents.
Following reconnaissance by drones after the latest strikes, Turkish artillery hit IS positions in Syria on Sunday, Anatolia said, adding that nine jihadists were killed.
Separately, Turkish police detained four suspected IS jihadists who were allegedly planning an attack on May Day celebrations in the capital Ankara, state media said.
Planned May Day events in the southern cities of Adana and Sanliurfa were also scrapped after the authorities reportedly received intelligence of a possible suicide bomb plot.