NATO announced Friday that six more U.S. troops have died in Afghanistan, bringing the death toll for July to at least 66 and surpassing the previous month's record as the deadliest for American forces in the nearly 9-year-old war.

In Kabul, police fired weapons into the air Friday to disperse a crowd of angry Afghans who shouted "death to America," hurled stones and set fire to two vehicles after an SUV, driven by U.S. contract employees, was involved in a traffic accident that killed four Afghans on the main airport road, according to the capital's criminal investigations chief, Abdul Ghaafar Sayedzada.

A statement issued by the U.S. Embassy in Kabul said a vehicle carrying four U.S. contract workers was involved in a two-car accident near the airport.

"Our sympathies go out to the families of those Afghans injured or killed in this tragic accident," the embassy said.

Witnesses said foreigners fled the scene, but the embassy said the contractors were cooperating with local Afghan security forces.

Afghan police, some carrying riot shields, converged on the area, firing warning shots into the air to disperse the protesters. Sayedzada said the crowd burned two foreigners' vehicles, causing heavy black smoke to rise from the scene.

"It is our right to raise up our voice and protest when innocent Afghans are harmed," said Azizullah, a 25-year-old student, who like many Afghans uses one name.

Ahmad Jawid, who also was at the scene, asked: "Are we not Muslims? Are we not from Afghanistan? Infidels are here and they are ruling us. Why?"

A fatal traffic accident caused by a U.S. military convoy in 2006 triggered an anti-American riot in Kabul that left at least 14 people dead and dozens injured.