KABUL, Afghanistan (AP) — A suicide bomber riding a motorcycle on Monday killed two Afghan defense ministry staffers and wounded at least nine others after he rammed into a bus carrying soldiers and civilian employees who were returning home from work.

Gen. Kadam Shah Sheem, Kabul military commander, said the bombing took place in eastern Kabul city and targeted a bus full of officers, soldiers and defense ministry staff that had just left a nearby military base. He said one of the dead was an officer and the other a civilian.

Afghan Defense Ministry spokesman Gen. Zahir Azimi confirmed the casualty numbers but had no other details.

An eyewitness, shopkeeper Mohammad Shakor, said the attack took place on a bumpy dirt road near a grave yard. He said the bus had just unloaded four women passengers and was driving away when the explosion took place.

Taliban spokesman Zabihullah Mujahid claimed responsibility for the attack in text message to The Associated Press.

President Hamid Karzai condemned the attack in an announcement issued by his office.

The Taliban have escalated their attacks against Afghan security forces and government employees ahead of a second round of voting next month to elect a news president.

A second round was forced after elections last month failed to give any candidate the majority needed to replace outgoing President Hamid Karzai.

Insurgents are seeking to take advantage of the full withdrawal of foreign combat troops this year in an effort to overthrow the government and regain territory lost in nearly 14 years of war.