Afghan police say a suicide bomber has blown himself up near a police vehicle in southern Afghanistan, killing at least four people.

Police say the explosion hit a vehicle carrying a police commander outside Qalat, the capital of Zabul province. It is is not clear if the official was among those killed.

Shortly before Thursday's attack, officials say a convoy of presidential bodyguards had passed through Qalat on the way back to the capital, Kabul. Witnesses say the convoy may have been the intended target of the bomber.

Afghan President Hamid Karzai was not in the convoy. He returned to Kabul by air today after making a rare visit to to southern Afghanistan.

In another development, NATO says it carried out an air strike Wednesday on a Taleban command post in Kandahar province. It says the attack in the Panjwayi district completely destroyed the compound and caused several Taleban casualties.

During Mr. Karzai's visit to Kandahar city this week, he accused Pakistan's government of directly supporting Taleban insurgents in Afghanistan.

Pakistani Foreign Minister Khursheed Kasuri responded Wednesday by saying Islamabad will do whatever it takes to bring stability to Afghanistan.

Some information for this report was provided by AFP, AP and Reuters.