A teenage suicide bomber managed to slip through tight security into police headquarters in Afghanistan's southern Kandahar province on Wednesday, but blew himself up before he could reach the police chief he was targeting, authorities said.

A policeman was wounded in the attack, which came less than a year after a suicide bomber successfully killed previous Kandahar police chief Khan Mohammad Mujahid in his compound, an attack the Taliban said they had ordered.

The assault raises concerns about security in an area that was the birthplace of the Taliban and has been a focus of efforts by a surge of U.S. troops to boost Afghan government control in the south.

The 15-year-old boy had a letter for me and wanted to meet me, police chief Abdul Raziq told reporters.

But as soon as he got near my office a policeman noticed he (had explosives) and started to shoot him, Raziq said, adding that the bomber detonated his explosives on the spot.

Raziq said an investigation was underway to see how the adolescent bomber managed to pass several layers of security with explosives strapped on his body.

Despite the presence of more than 100,000 foreign troops, violence across Afghanistan remains at its worst levels since the Taliban were toppled by U.S.-backed Afghan forces in late 2001, according to the United Nations.

On Tuesday, three suicide bombers stormed a government building in eastern Paktika province, killing four government employees and three policemen. The Taliban claimed responsibility for the assault.

Foreign forces fighting Taliban-led insurgents in Afghanistan are in the process of handing control of security over to the Afghan army and police, with foreign combat troops due to leave by the end of 2014.

(Reporting by Ismail Sameem, writing by Mirwais Harooni; Editing by Amie Ferris-Rotman and Yoko Nishikawa)