KABUL, Afghanistan (AP) -- Protesters angry over Quran burnings by American troops lobbed grenades at a U.S. base in northern Afghanistan and clashed with police and troops in a day of violence that left seven international troops wounded and two Afghans dead.

The top American diplomat in the country said the spike in tensions between the U.S. and Afghanistan caused by the Quran burnings, including the killing of two American military advisers Saturday at an Afghan ministry, would not diminish Washington's commitment to the region.

"Tensions are running very high here and I think we need to let things calm down, return to a more normal atmosphere, and then get on with business," Ambassador Ryan Crocker told CNN's "State of the Union."

Sunday's violence was the latest in six days of riots across the country by Afghans furious at the way some Qurans at an American base outside of Kabul were disposed of in a burn pit. The incident has swiftly spiraled out of control, leaving dozens of people dead, including four U.S. troops reportedly killed by their Afghan counterparts.

Afghan authorities have launched a manhunt across the country for a driver they suspect of killing the two U.S. military advisers at the Interior Ministry. International advisers working at Afghan ministries were recalled out of fears of another attack.

In Kunduz province, thousands of demonstrators started out protesting peacefully Saturday but then turned violent as they tried to enter the district's largest city, said Amanuddin Quriashi, district administrator. People in the crowd fired on police and threw grenades at a U.S. base on the city outskirts, he said.

Seven NATO troops were wounded by the grenade. One protester was killed when troops fired out from the U.S. base, and another was killed by Afghan police, Quriashi said. Provincial police spokesman Sarwar Hussaini confirmed the casualties.

A NATO spokesman said that an explosion occurred outside the base, but that the grenades did not breach its defenses.

"Initial reports indicate that there were no ISAF service member fatalities," said Navy Lt. Cmdr. Brian Badura, referring to NATO's International Security Assistance Force. He declined to comment on whether there were any wounded.

More than 30 people have been killed in clashes since it emerged Tuesday that copies of the Muslim holy book and other religious materials had been thrown into a fire pit used to burn garbage at Bagram Air Field, a large U.S. base north of Kabul.

The death toll from the unrest includes the two slain military advisers as well as two U.S. troops killed last week by an Afghan soldier.

NATO, Britain and France recalled their international advisers from Afghan ministries in the capital after the two advisers - a lieutenant colonel and a major - were found dead in their office, shot in the back of the head.

The main suspect in the shooting is an Afghan man who worked as a driver for an office on the same floor as the advisers, Interior Ministry spokesman Sediq Sediqi. He did not provide further details about the man or his possible motive.

The Taliban claimed that the shooter was one of their sympathizers and that an accomplice had helped him get into the compound to kill the Americans in retaliation for the Quran burnings.

President Barack Obama and other U.S. officials have apologized for the burnings, which they said were a mistake. But their apologies have failed to quell the anger of Afghans, who see the Quran burnings as an illustration of what they perceive as foreign disrespect for their culture and religion.

Afghan President Hamid Karzai renewed his calls for calm in a televised address to the nation.

"Now is the time to return to calm and not let our enemies use this situation," he said.

He added that the unprecedented recall of NATO staff was understandable, saying that "it is a temporary step at a time when the people of Afghanistan are angry over the burning of the holy Quran."

Members of the international military coalition described the removal of advisers as a temporary security measure, stressing that they did not expect it to affect partnerships with the Afghans that are key to preparing the country's security forces to take on more responsibility as international troops draw down.

"We continue to move forward and stand by our Afghan partners in this campaign. We will not let this divide the coalition," said Lt. Col. Jimmie Cummings, a spokesman for the international force. The NATO recall affects advisers numbered "in the low hundreds," Cummings said.

The U.S. government had already ordered its government advisers to stay inside the secure embassy compound earlier in the week out of fear of retribution, said Gavin Sundwall, a U.S. Embassy spokesman.

In Berlin, Defense Ministry spokesman Stefan Paris said late last week that it had withdrawn troops early from an outpost in northern Afghanistan because of the protests.

Paris said the German military, which handed over security responsibility for the Taloqan area to Afghan authorities on Feb. 15, originally planned to shut down its base there altogether in late March. He said the regional commander decided to pull the remaining 50 German troops back to a large base in Kunduz because of the demonstrations in the Taloqan area.

Germany has nearly 4,800 troops in northern Afghanistan.

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