A suspected car bomb exploded across a secondary school in the Turkish capital on Tuesday, wounding 15 people, authorities said.

There was no immediate claim of responsibility, but the attack comes at a time when Kurdish rebels fighting for autonomy in southeastern Turkey have escalated their attacks on Turkish targets. The rebels carried out deadly bomb attacks in Turkish cities in the past. Islamic and leftist militants were also behind some bombings in this NATO-member and U.S. ally country.

"There is information that a bomb was planted on the vehicle," that exploded in the downtown Kizilay district, said Deputy Prime Minister Bulent Arinc.

The blast wounded 15 people, said Besir Atalay, another deputy prime minister. At least three of the injured were in serious condition and some of them reportedly lost their limbs.

"I felt the blast effect of the explosion some 500 meters (547 yards) away," said Ekrem Erkoc, a 42-year-old eyewitness. "I saw vehicles on fire and an injured man said people lost their limbs."

The injured were initially treated in the school yard before medics rushed to the scene and whisked them away to hospitals, NTV television said.

Kurdish rebels were last blamed for a small bomb attack in the Mediterranean resort town of Kemer on Aug. 28 that injured 10 people, including four Swedish nationals.

Kurdish rebels have been fighting for autonomy in Turkey's mainly Kurdish southeast since 1984.

Turkish warplanes have bombed suspected rebel hideouts in northern Iraq last month in response to an escalation of attacks by the guerrillas. Turkey has not ruled out a cross-border offensive against Kurdish rebel bases in northern Iraq.