A car bomb Sunday hit the Turkish city of Gaziantep, a major refugee hub near the Syrian border, killing at least one policeman and wounding 13 people, with the country on edge after a succession of militant attacks. In a separate attack in the province of Mardin to the east, three Turkish soldiers died in an ambush by Kurdish militants who have killed hundreds of members of the security forces in a renewed insurgency since last year.Gaziantep regional governor Ali Yerlikaya said in a statement quoted by the state-run Anatolia news agency that nine of those wounded in the attack in the city were police and the explosion was caused by a car bomb.NTV television said there were sounds of gunfire as clashes erupted with the security forces. Security camera footage published by Turkish media showed the moment the bomb went off outside the gates of the multi-storey police building.Television pictures showed chaotic scenes outside the imposing police headquarters in Gaziantep as ambulances rushed to help wounded lying on the ground.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 attack comes with Turkey on edge after two deadly attacks in Istanbul this year blamed on Islamic State (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.However there was no immediate indication over who could have carried out the attack in Gaziantep.The outlawed Kurdistan Workers Party (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.A female suicide bomber on Wednesday blew herself up in the former Ottoman capital of Bursa, south of Istanbul.Press reports have suggested a link with the PKK but the authorities have so far remained tight-lipped on which group was behind the Bursa attack.However violence has rarely touched the Gaziantep region, which lies to the west of Turkey's main Kurdish-dominated areas.Three Turkish soldiers were killed and 14 others wounded in the attack on Sunday in Kurdish-dominated Mardin province to the east of Gaziantep, which was carried out by 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.Gaziantep is seen as vulnerable to attacks by IS jihadists who still control parts of Syria on the other side of the border, despite an offensive by Kurdish militias.Also on Sunday, four people were wounded in the Turkish town of Kilis, just south of Gaziantep on the Syrian border, by rockets fired from an IS-controlled area of Syria, Anatolia said.Kilis has regularly been hit by sometimes deadly rocket attacks by IS over the last months, prompting anxiety and anger on the part of 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.Police security was also stepped up across Turkey on Sunday as Turkish leftist and labour activists prepare to celebrate May Day, an event that often ends in clashes with security forces...