In a statement, the White House said, "both leaders deplored the desecration of the Koran, strongly condemned the April 1 attack on (the United Nations compound) in Mazar-i-Sharif and expressed deep regret for the tragic loss of life."

"The two presidents were clear that to attack and kill innocent people is an affront to human decency and dignity," it also said.

A mob attacked United Nations bureaus on 1 April, killing three officials and four Nepali soldiers protecting them. Altogether at least 24 people, including many Afghans, were killed and many more injured.

Karzai’s office released a statement about the videoconference that differed somewhat from that of the White House.

Karzai's office said that the two presidents discussed “the desecration of the Koran by the American pastor and the subsequent unpleasant incidents that followed in Afghanistan”.  It also noted that Obama "strongly condemned the desecration of the Koran by an American pastor and regretted the casualties at protests in Mazar-i-Sharif and Kandahar."

The incident confirms growing tensions between Karzai and his Western allies. Experts note that protests in Afghanistan over the burning of the Qur‘an occurred eight days after Karzai condemned the act as "disrespectful and abhorrent."

The violence comes as Afghan forces are due to assume control of security in a handful of Afghanistan's safer areas—including Mazar-i-Sharif—in July, allowing the withdrawal of the 130,000 foreign troops to begin. Afghan forces are due to take complete control across the country in 2014.

Local sources suggest that protests were initially provoked by afghan political circles vying for support among a population that is extremely devout and religious but living in abject poverty and lacking in essential services. Protests have continued but have been peaceful and more political in nature.

Today in Kabul after morning prayers, 300 people protested in front of the Eid Gah Mosque. With police present, protesters carried banners and placards bearing slogans that include “Murder, murder America” and the “Koran is our law”.

In Qalat, Zabul Province, protests have taken a violent turn. The same is true in Nimroz Province and elsewhere.

After a woman was killed in a car accident in Kabul involving a NATO military convoy, protesters threw stones at the international forces.

“Those in power have an interest in the protests,” a source told AsiaNews, “and in a broad anti-Western attitude. The people have little sympathy for the Western military presence, and those in power are encouraging this even if it is risky because the Taliban might take advantage of the situation. The West for its part does not react to it, limiting itself to condemning the violence without looking for its real cause.”