Five policemen were killed and four were missing after suspected militants attacked a vehicle checkpoint early Monday on a highway leading to southern Afghanistan's main city, a highway officer said.

The 2 a.m. attack was on a checkpoint in Zabul province outside the city of Qalat on the main highway between Kabul, the capital, and the southern city of Kandahar, said a highway police official.

He said five officers were killed, one was wounded and that four were missing.

The official spoke only on condition of anonymity because he was concerned Interior Ministry officials did not want him to speak about it publicly. It was not immediately possible to confirm with local or provincial police chiefs because new officials were being assigned to the posts as part of a sweeping shake-up announced after last week's deadly riots in Kabul.

An Interior Ministry official said he thought the attack on the police checkpoint had happened but that the ministry could not get in contact with police officials to confirm it. He also asked not to be identified, citing ministry policy because he was not the lead spokesman.

Militants have stepped up attacks in recent months, particularly in Afghanistan's southern and eastern regions.

CountryWatch: Afghanistan

In neighboring Uruzgan province on Monday, a firefight between suspected Taliban militants and police left two militants dead, said Allah Ullah Khan, a district police chief. Six militants were also arrested, he said.