A suicide bombing killed four Afghan personnel of a U.S. security company in Kandahar province of southern Afghanistan on Sunday, a local police officer Mohammad Asaf told Xinhua.

A bomber driving a motorbike blew himself up on a highway in Spin Boldak district when a vehicle of the U.S. Protection and Investigations (USPI) was passing, Asaf said.

Three guards and one driver of the USPI, which is a private U.S. security company, were killed in the blast, he added.

No one has claimed responsibility, but Taliban militants have frequently carried out similar attacks.

The USPI has been attacked by militants in this country from time to time.

A suicide bombing killed two American and five Afghan USPI staff at the gate of its office in Kandahar city, capital of Kandahar province, on Dec. 6, 2006.

Spin Boldak, a district bordering Pakistan, has witnessed much violence over the past year.

A suicide blast killed three civilians and injured eight others at a police checkpoint in the district on March 13, 2007.

Taliban commanders claimed 2,000 suicide bombers would launch a bloody spring offensive against foreign troops and other targets in the country this year.

As it gets warmer, Afghanistan has suffered much more Taliban- linked violence.

A total of 12 soldiers of the NATO-led International Security Assistance Force (ISAF) have been killed in combat in this volatile country over the past week.

Due to rising Taliban-linked insurgency, over 800 persons have been killed in Afghanistan this year.

Source: Xinhua