U.S. Secretary of State Hillary Clinton has for the first time explicitly linked al-Qaida's North African branch to the attack at the U.S. diplomatic mission in Libya that killed four Americans, including Ambassador Christopher Stevens.

Clinton told a special United Nations meeting on North Africa's Sahel region Wednesday that al-Qaida in the Islamic Maghreb is using the area as a haven to support extremism and terrorist violence in countries like Libya.

She said the regional al-Qaida group is working with other violent extremists “to undermine the democratic transitions under way in North Africa, as we tragically saw in Benghazi.”

The top U.S. diplomat also said American intelligence and law enforcement agencies are increasing their cooperation with regional countries to investigate the September 11 attack in Benghazi.

In her remarks, Clinton did not offer any specific, new evidence to indicate the attack might not have been the local, spontaneous eruption of violence that the administration initially described.

Earlier Wednesday, Libyan President Mohammed el-Magarief also characterized the deadly attack on the U.S. consulate as a “pre-planned attack of terrorism.”

In an interview with U.S.-based NBC News, Mr. Magarief said the attack had nothing to do with protests against an anti-Islam film.

“It was launched with a high degree of accuracy, which means that the perpetrators must have had some kind of exercise on how to hit, how to launch this act.”

From the beginning, Libyan officials have pointed to foreign involvement in the assault, even as they are attempting to crack down on the extremist militias that clearly had a role in the attack.

The White House said Wednesday that President Barack Obama also considers the incident a terrorist strike.

The assault took place on the anniversary of the September 11, 2001 terrorist attacks in the United States as thousands of Muslims were protesting a video produced by a California-based anti-Muslim filmmaker.

In a speech Tuesday to the U.N. General Assembly, Mr. Obama called the video “crude” and “disgusting.” But he said no video justifies an attack on U.S. property.