An Afghan soldier has shot dead two NATO troops, after joining protests against the burning of the Koran at a NATO air base. The dead troops were Americans.
Protests against the burning of the Koran drew thousands of Afghans to the streets on Thursday for a third consecutive day. So far, 11 people have been killed and many more wounded.
The incident has led to the Afghan Taliban calling on security forces to turn their guns on foreign infidel invaders.
President Barack Obama has sent a letter to President Hamid Karzai apologising for the incident, saying it was a genuine mistake.
A French military base to the east of Kabul has also been attacked.
Muslims consider the Koran the literal word of God and treat each book with deep reverence.
Afghan labourers found charred copies of the Koran while collecting rubbish at Bagram airbase.
Officials at Bagram reportedly believed Taliban prisoners were using the books to pass messages to each other.
A BBC reporter in Kabul says Friday prayers may spark more tensions.