ANKARA, Turkey (AP) — A car bomb struck the entrance of a Turkish police station Sunday in the southern city of Gaziantep, killing a policeman and injuring 23 other people, an official said.

Gov. Ali Yerlikaya of Gaziantep province issued a statement saying 19 policemen and four civilians were wounded in the explosion that went off at 9:17 a.m. There was no immediate claim of responsibility for the attack.

Unconfirmed reports say gunfire was heard after the blast, which shattered the windows of nearby buildings. Several ambulances were sent to the scene, the private NTV television reported.

The police station is close to several government offices, including that of the governor and mayor. The area is normally crowded but was empty early Sunday. May 1 International Labor Day demonstrations in the city were canceled for security reasons, the private Dogan news agency reported.

In the Turkish capital, Ankara, police carried out anti-terrorism operations overnight and detained four suspected IS members allegedly planning to attack demonstrators observing Labor Day, the state-owned Anadolu Agency reported.

Turkey, which is facing both growing blowback from the conflict in Syria and renewed conflict with Kurdish militants, has seen a rise of such attacks recently. In the past year, more than 200 people across the country have been killed in six major bombings. This week a female suicide bomber blew herself up in the city of Bursa, northwest Turkey, in attack that ended her life and wounded 13 people.

In a separate incident Sunday, four people were wounded after two rockets hit a car park and house garden in Kilis, another town near the Syrian border, Anadolu Agency reported. It said the Turkish military retaliated by firing at IS targets across the border in Syria, killing nine militants. It was not possible to verify the agency's claim.