US President Barack Obama has apologised to the Afghan people for the burning of Korans by American troops at a US base.
In a letter to President Hamid Karzai, Obama has expressed his deep regret and said the incident earlier this week was a genuine mistake.
Obama's letter, delivered by the US ambassador to Afghanistan, assured the Afghan president that US authorities would question all those responsible.
Demonstrations against the desecration have continued for a third day across northern and eastern Afghanistan.
Two US soldiers and two Afghans were killed in an attack on a military base.
Elsewhere there were four other deaths.
On Wednesday, another seven people were killed and dozens injured in protests.