Militants launched two attacks against Afghanistan's vulnerable police, killing eight officers including four who were destroying a field of opium poppies, officials said Sunday.

The attack against the eradication team in Kandahar province's Maiwand district Saturday was at least the third time militants have attacked efforts to destroy opium poppies in the last several weeks. A week ago, fighters killed seven police who were eradicating poppies.

Kandahar police chief Sayed Agha Saqib has said police would increase protection levels around the teams. Around 100 police on the country's poppy-eradication force were killed in the line of duty over the last year, the Interior Ministry has said.

Militants or criminal gangs are attacking the police eradication teams to protect a business that provides them with tens of millions of dollars a year. Afghanistan supplies more than 90 percent of the world's illicit opium, the main ingredient in heroin. Taliban fighters and criminals collect protection fees from farmers and traders for safe passage of the crop.

Farmers cultivated a record 477,000 acres of opium in 2007, a 14 percent increase over the previous year. Total production, spurred by unusually high rainfall, increased even further, by 34 percent, to 9,000 tons, the U.N. has said.

Elsewhere in the south, Taliban fighters attacked a police checkpoint in the Gereshk district of Helmand province Saturday night, said district police chief Khair Uddin Shuja.

Police dispatched backup to the checkpoint, but Taliban militants ambushed one of the police trucks, killing four officers and wounding seven, he said.

Militants killed more than 900 police officers last year. Police are inviting targets because they have less training and weaponry and work in smaller teams than Afghan or NATO soldiers.

Last year was the most violent in Afghanistan since the 2001 ouster of the Taliban regime by a U.S.-led coalition. More than 8,000 people, mostly militants, died in insurgency related violence, the U.N. says.