KABUL: A bus carrying Afghans working for a U.S.-supported demining group was struck by a roadside bomb in Kandahar province Sunday, killing five workers and wounding 13 others.

Also Sunday, NATO said an Afghan soldier shot and lightly wounded a Polish soldier with whom he had been arguing. The Afghan soldier fled after the shooting and was being sought by Afghan and international forces.

Meanwhile, NATO reported a member of the international security force was killed by a roadside bomb in southern Afghanistan. No other details were given in keeping with standard procedure.

The bus belonging to the Demining Agency for Afghanistan was struck early Sunday as it traveled through Kandahar province's Daman district, according to Mohammed Ibrahim, chief of medicine at Kandahar Hospital.

Roadside bombs are a signature weapon of the Taliban in their struggle against foreign forces and the Afghan government, but more often kill Afghan civilians. It wasn't clear if the blast was random or specifically targeted the demining agency, known as DAFA, which receives more than half its funding from the U.S. State Department, according to its Web site.

The group clears mines across southern Afghanistan that are a legacy of 25 years of near-continuous warfare and continue to kill scores of Afghans each year.

The unidentified Pole shot Saturday night at a joint command center in the eastern province of Ghazni was transferred to a medical facility for treatment, according to a NATO spokesman in Kabul, speaking on routine condition of anonymity.

The Ghazni base is headquarters of the 2,600 Polish troops stationed in Afghanistan as part of the NATO effort to root out Taliban remnants and extend the central government's remit into rural areas.

While rare, Afghan troop attacks on international forces risk damaging the trust between Afghan police and soldiers who work side-by-side with their foreign mentors on training and combat missions. An Afghan soldier killed a U.S. service member and wounded two Italian soldiers in December in the western province of Badghis, about one month after a rogue policeman in Helmand province shot and killed five British soldiers.

Afghan Defense Ministry spokesman Mohammad Zahir Azimi said the shooting resulted from an argument between the two men, but details weren't immediately known. He said both had pulled weapons and fired, but only the Polish soldier was wounded. The whereabouts of the Afghan soldier weren't known, and it was possible he was hiding somewhere on the base, Azimi said.

"It seems to have been a fight and the soldier was operating on his own," Azimi said.

Zabiullah Mujahid, a spokesman for the Taliban, said the Afghan soldier had escaped, killing four Afghan soldiers in the process, and was now with the insurgents. The claim could not be verified, and the Taliban has a history of making false and exaggerated claims.

Also Sunday, Interior Ministry spokesman Zemari Bashary said investigators were questioning three Italian medical workers detained the day before as part of an investigation into an alleged plot to kill the governor of Helmand province. They were among nine people held after suicide bomb vests, hand grenades, pistols and explosives were discovered in a hospital storeroom in Helmand's capital Lashkar Gah.

"We need to question a number of people to find out who brought the materials to the hospital and for what purpose," Bashary said.

Emergency, the Milan-based organization that runs the hospital, has denied involvement in any plot.

Bashary said the investigation would proceed cautiously in recognition of the work done by Emergency, which has operated in Afghanistan since 1999 and runs three operating theaters, a maternity hospital and 28 health centers.

Emergency has had a tense relationship with local authorities in violence-wracked Helmand, due in part to its policy of treating all patients, including those who may be Taliban.

Helmand's governor, Gulab Mangul, alleged Saturday that Taliban insurgents had paid hospital authorities $500,000 to kill him, but Bashary said the ministry could not confirm that charge.