Police in Pakistan say a suicide bomber on a motorcycle has struck a bus carrying employees of the country's nuclear agency, killing two people and wounding several others.

Police officer Mohammad Aslam said Thursday's attack targeted a bus of the Pakistan Atomic Energy Commission in the Punjab province. He says the assailant opened fire on the bus, prompting the driver to stop the vehicle and chase him. The attacker then set off his explosives.

No one immediately claimed the attack.

Pakistan tested its first nuclear weapon in 1998, in response to a similar move by its archrival India.