A homicide bomber in Afghanistan killed a British soldier and two children Thursday, while another killed a policeman. President Hamid Karzai urged NATO forces to use caution a day after 20 civilians died.

NATO's International Security Assistance Force said the homicide attack in southern Helmand province's Lashkar Gah town wounded two British soldiers, and Britain's Ministry of Defense said one later died of his wounds.

The bomber hit a British jeep, which was engulfed in flames after the blast. The explosion also killed two children — a boy and a girl, both under the age of 8 — and wounded seven civilians, said Ghulam Muhiddin, the spokesman for Helmand's governor.

In the eastern province of Khost, a homicide bomber hurled himself in front of a police car, killing a policeman and wounding four others, said the provincial police chief, Gen. Mohammad Ayub.

Afghanistan this year has faced the deadliest spate of violence since U.S.-led forces ousted the Taliban regime five years ago.

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Militants have increasingly resorted to the use of suicide and roadside bombs, particularly in the south and east near the Pakistan border.

President Hamid Karzai, meanwhile, said that while Afghanistan is "committed to the fight against terrorism," NATO forces need to take precautions during military operations to protect civilians.

Karzai said nine civilians were killed and 11 wounded during a battle Wednesday in Kandahar province's Ashogho town. He also said 11 civilians were killed during a fight the same day in Tajikan village in Helmand province.

"I have mentioned this several times in the past that every effort should be made to ensure the safety of civilians and that inflicting harm to them is not acceptable to us," the president said in a statement. "Once again, I urge NATO forces to take maximum caution during their military operations to avoid harming civilians."

NATO Secretary-General Jaap de Hoop Scheffer, meanwhile, said additional NATO forces are needed in Afghanistan to supplement the 31,000 currently in the country, and that the NATO mission will only succeed if it can help the Afghan government improve ordinary people's lives.

De Hoop Scheffer told BBC radio that suicide attacks show that the Taliban can only be "spoilers" in the process of nation building. "I can assure you they will not beat NATO, neither the U.K. nor other forces, by employing these tactics," he said.

Karzai conveyed his sympathies to the civilian victims' families, and instructed the Kandahar and Helmand governors to provide emergency assistance to those in the two incidents.

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Ashogho residents said NATO helicopters fired on three mud homes where villagers were sleeping. NATO said the operation, targeting militants suspected in roadside bombings, was believed to have caused several civilian casualties, which it regretted.

In Tajikai, in Helmand province's Grishk district, a rocket hit a house during a nighttime clash between suspected Taliban insurgents and NATO and Afghan security forces, police said.

Karzai's statement said 11 civilians were killed, but Abdul Rehman, a resident, said 13 villagers, including 10 women and children, died in rocket fire from an aircraft.

NATO said its aircraft and helicopters had fired on a "positively identified" compound from where the suspected Taliban were firing rocket-propelled grenades and automatic weapons.

"Initial bomb damage from an observer on the ground confirmed a direct hit on the compound," the statement said. NATO said it will "fully investigate" the claim that civilians were killed in the strike.

Since late 2001, there have been numerous incidents of civilians killed in military operations against Taliban and Al Qaeda fighters, although U.S.-led coalition and NATO forces say they go to extreme lengths to avoid civilian casualties.

The international troops accuse insurgents of blending in with local populations while attacking foreign and Afghan soldiers. Many other civilians have been killed in Taliban attacks, including scores in recent suicide bombings.