Pakistani officials say gunmen have attacked a school bus in northwest Pakistan, killing four children and the driver.

At least 16 other people, most of them children, were wounded in Tuesday's attack near the city of Peshawar, close to Pakistan's border with Afghanistan.

Police say militants first aimed a rocket at the school bus and missed, then opened fire. The bus was taking children home from school at the time.

The Taliban claimed responsibility for the attack. A Taliban spokesman said the children on the bus were from a local tribe that has been fighting insurgents in the region. He warned that Taliban militants will continue to carry out similar attacks.

U.N. Secretary-General Ban Ki-moon condemned the attack, calling it an “abhorrent act of terrorism.” He extended his condolences to the families of the victims.

The area where the attack occurred is a stronghold of al-Qaida and Taliban-linked militants who have targeted civilians in the past.

Separately, police say the head of the main ruling party in northwest Pakistan was killed Tuesday in a roadside bombing near the Swat Valley, once controlled by the Taliban. Sher Khan, leader of the Awami National Party, was in a vehicle when the bombing took place. A police official says Khan's driver and guard were wounded in the attack.