KANDAHAR, Afghanistan - Taliban militants ambushed a truck full of Afghan police in southern Afghanistan, killing four officers and injuring three, while a separate gunfight left 11 Taliban fighters dead, officials said Saturday.

The attack occurred Friday evening in the Panjwayi district of Kandahar province, said provincial police chief Afmatullah Alizai.

Panjwayi was the scene of NATO's largest ground battle in September, when alliance forces killed more than 500 militants, largely clearing the region of insurgents.

Canadian and U.S. Special Forces are now working in Panjwayi to increase security. More Afghan security checkpoints have been put up, a new road is being built and schools and clinics are reopening.

But small groups of fighters remain.

The attack on the police happened near the village of Talukan. Militants in December beheaded two men in Talukan, saying the two were working with NATO forces.

In nearby Helmand province, a convoy of NATO and Afghan troops came under fire, touching off a four-hour gunbattle that left 11 Taliban dead, according to provincial Police Chief Ghulam Nabi Malakhail.

The Taliban took their dead fighters off the battlefield, but officials obtained the casualty numbers through intelligence contacts, Malakhail said.

On Saturday, a suicide bomber detonated his vehicle near a NATO convoy outside Kandahar city, killing himself but hurting no one else, Alizai said.

Attacks spiked in Afghanistan last year, with some 4,000 people killed in insurgency-related violence, according to an Associated Press count based on numbers from U.S., NATO and Afghan officials.

NATO officials are bracing for more violence this spring, when fighters typically step up attacks after a winter lull.