The probe into a possible friendly fire incident further aggravates already strained relations between Afghan President Hamid Karzai and the international community, which holds his enfeebled government partly responsible for rising instability.

After enduring a drumbeat of criticism from world leaders in recent days, the Afghan government struck back on Saturday, saying it viewed a U.N. official's prescription for ridding the country of corruption and warlords as an infringement on its national sovereignty.

The airstrike occurred Friday during heavy fighting in Badghis province, a remote area that borders Turkmenistan. Two days earlier, two American paratroopers disappeared there while trying to recover airdropped supplies that had fallen into a river. Fighting broke out between members of a search team and Taliban insurgents, the U.S. military said.

Eight Afghans - four soldiers, three policemen and an interpreter - were killed. Seventeen Afghan troops, including soldiers and police, five American soldiers and another Afghan interpreter were wounded, the U.S. said.

Afghanistan's Defense Ministry said the deaths and injuries likely happened "during an air attack by NATO forces" on a joint U.S.-Afghan base.

U.S. officials would not confirm the account, but said in a statement that a joint investigation was under way to determine whether any of the casualties were caused by NATO "close air support."

The top U.S. and NATO commander, Gen. Stanley McChrystal, has ordered commanders to use airpower sparingly to minimize civilian casualties, which threaten to undermine Afghan support for the war against the Taliban. However, commanders are free to call in airpower to defend themselves against Taliban attack.

Although the U.N. says most civilian casualties have been at the hands of militants, deaths of men, women and children in NATO airstrikes have raised tensions between Karzai's government and the U.S.-led coalition - already running high because of widespread corruption and drug trafficking that have proliferated in the last four years.

Since a presidential election marred by fraud returned Karzai to power, a host of international figures, including President Barack Obama and British Prime Minister Gordon Brown, have called on the Afghan leader to take concrete steps to clean up his government.

On Friday, Kai Eide, head of the U.N. mission in Afghanistan, lectured the Karzai government, saying "we can't afford any longer a situation where warlords and power brokers play their own games." "We have to have a political landscape here that draws the country in the same direction, which is in the direction of significant reform," Eide said.

Eide said members of Karzai's new government should be vetted not just for ties to insurgent groups but also for links to criminal or drug activity. Karzai's running mate, a former Tajik warlord, has repeatedly denied allegations that he has been involved in drug smuggling.

His remarks drew a sharp rebuke Saturday from the Afghan Foreign Ministry, which accused Eide and others of interfering in the makeup of the new Karzai government.

"Over the last few days some political and diplomatic circles and propaganda agencies of certain foreign countries have intervened in Afghanistan's internal affairs by issuing instructions concerning the composition of Afghan government organs and political policy of Afghanistan," the ministry said. "Such instructions have violated respect for Afghanistan's national sovereignty."

Karzai promised in his first speech after his victory that he would work to eliminate corruption, but did not give any specific proposals. During an interview with The Associated Press, Foreign Ministry spokesman Ahmad Zahir Faqiri called the U.N. official's comments "unfair."

"The elected president of Afghanistan, after his re-election, made some remarks to say he is committed to combatting corruption, to expand the rule of law," Faqiri said. "These were very important points."

He said details about the anti-corruption measures would be made public along with Cabinet appointments in about two or three weeks.