Protesters angry over Qur'an 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 attacks were the latest in six days of violence across the country by Afghans furious at the way some Qur'ans at an American base outside of Kabul were disposed of in a burn pit. The incident has swiftly spiralled out of control leaving dozens of people dead, including four U.S. troops killed by their Afghan counterparts, in a sign of the tenuous nature of the relationship between Afghanistan and the U.S.

A U.S. military convoy enters the Afghan Interior Ministry in Kabul, where a gunman killed two American advisers on Saturday. (Musadeq Sadeq/Associated Press)

Afghan authorities have launched a manhunt across the country for a driver they suspect in the killing of two U.S. military advisors who were shot to death at an Afghan ministry a day earlier. International advisers working at Afghan ministries were recalled out of fears of another attack.

In Kunduz province, thousands of demonstrators started out protesting peacefully but then the group 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 and one of the protesters was killed when troops fired out from the U.S. base, Quriashi said. Another demonstrator was killed by Afghan police, he added. Provincial police spokesman Sarwar Hussaini confirmed the casualties.

Explosions outside base confirmed

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

"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 days of unrest includes four U.S. soldiers — two killed last week by an Afghan soldier, and two military advisers shot Saturday at the Interior Ministry.

NATO and the British government recalled their international advisers from Afghan ministries in the capital late Saturday after the two advisers — a lieutenant colonel and a major — were found dead in their office, shot in the back of the head. The names of the victims have not been released.

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' office, Interior Ministry spokesman Sediq Sediqi. He did not provide further details about the man or his possible motive.

The Canadian Embassy has suspended all meetings at Afghan ministries and continues to monitor the situation closely, Foreign Affairs spokesman Yohan Roderick told CBC News.

The embassy is continuing to operate normally, he said.

With files from CBC News