A car bomb struck the entrance of a Turkish police station Sunday in the southern city of Gaziantep, killing two police officers and wounding 22 other people, according to the state-run Anadolu Agency.

Four civilians were among those injured in the 9:17 a.m. explosion, according to Gov. Ali Yerlikaya of Gaziantep province. The blast shattered the windows of nearby buildings.

The police station is close to offices for the governor and mayor. Gaziantep is also home to the offices of international aid organizations focused on the conflict in neighboring Syria.

There was no immediate claim of responsibility for the attack. Turkey has suffered multiple bombings in recent months linked either to Kurdish militants or the Islamic State group.

May 1 International Labor Day demonstrations in Gaziantep were canceled for security reasons, the private Dogan news agency reported.

Speaking in Ankara, the Turkish capital, Prime Minister Ahmet Davutoglu expressed his condolences and wished a speedy recovery to those wounded in "the heinous terrorist attack."

Police in Ankara, meanwhile, carried out anti-terror operations overnight and detained four suspected IS members allegedly planning to attack May Day demonstrators, the Anadolu Agency reported. In Istanbul, police imposed tight security measures and used water cannons and tear gas on May Day demonstrators who sought to rally in non-designated areas.

Turkey, which is facing both growing blowback from the conflict in Syria and renewed conflict with Kurdish militants, has seen a rise of deadly attacks across the country. In the past year, more than 200 people across the country have been killed in six major bombings.

In a separate incident Sunday, four people were wounded after two rockets hit a car park and a house garden in Kilis, another town near the Syrian border, the 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.