Local Afghan officials say three Afghan women working for an aid agency were shot dead when their car was attacked in the northern province of Jawzjan.

Their driver was also killed in Tuesday's attack.

Separately, U.S. officials say two Afghans employed by a U.S. firm were killed by a roadside bomb in northern Badakhshan province. Two Americans were also wounded in the incident.

Afghan protesters throw stones at a US military vehicle after traffic accident in Kabul, May 29, 2006

Meanwhile, Afghanistan's capital, Kabul, was peaceful but tense, a day after what appeared to be the worst riots there since the Taleban was ousted in 2001.

The U.S. military says the road crash that sparked the riots was caused by brake failure in a heavy military cargo truck. Afghan police say 12 people, including one policeman, died in the accident and the riots that followed.

Police say some 100 people were injured and 140 people were arrested. Kabul is now under curfew for the second straight night.

In other news, NATO's secretary general said operations in Afghanistan are the alliance's top priority. Jaap de Hoop Scheffer also said he hopes NATO will have completed its planned expansion of peacekeeping forces in Afghanistan in the next six months.

There are 9,000 NATO-led troops in Afghanistan, with plans to increase to 21,000 troops.

Some information for this report was provided by AFP, AP and Reuters.