The spreading violence comes as outrage grows over an obscure movie made in the United States called "Innocence of Muslims" that mocked Islam's Prophet Muhammad.

Speaking to reporters in Brussels after a meeting with European Union leaders which mainly focused on Egypt’s need for financial and economic aid and the situation in the Middle East, Morsi said that Egyptians "reject any kind of assault or insult against our prophet. I condemn and oppose all who insult our prophet."

But he added that this was "no justification for attacking embassies and killing innocent people." "We firmly condemn assaults against embassies. The Egyptian people will not engage in these ... unlawful acts," Morsi said. "It’s our duty top protect visitors and foreigners in Egypt," he added. 

Morsi said he had spoken to US President Barack Obama and condemned "in the clearest terms" the attacks on the U.S. consulate in Benghazi in which the ambassador and three other Americans died.

"We condemn strongly all those who launch such provocations and who stand behind that hatred," Morsi said, adding that he had asked Obama "to put an end to such behavior."

Crowds protesting at the U.S. Embassy in Cairo the same day as the Benghazi attack climbed its walls and tore down an American flag, which they replaced briefly with a black, Islamist flag. 

The protests continued on Thursday, with protesters clashing with police near the U.S. mission.

Protesters in Yemen, meanwhile, stormed the U.S. Embassy in Sanaa.

Officials were investigating whether the Libya rampage was a backlash to the video or a plot to coincide with the anniversary of the Sept. 11 terrorist attacks.

During his Brussels visit, the first to the West by the first democratically elected Egyptian president,  Morsi met with EU Council President Herman Van Rompuy, European Commission President Jose Manuel Barroso and foreign policy chief Catherine Ashton. "We had constructive talks," Morsi insisted. "We very much value the EU support for the democratic transition in Egypt," he said. 

Barroso said the EU is prepared to make available €500 million ($645 million) in financial assistance to Egypt to support the consolidation of democracy.

The EU is Egypt's largest trade partner and largest source of foreign investment. The two sides agreed that a joint EU-Egypt task force would meet later this year to find ways to further economic cooperation.

The EU already has made available €449 million to Egypt for the period 2011-2013, Barroso said.

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During the joint press briefing with Van Rompuy, Morsi said both agreed on the need to "put an end to the bloodshed in Syria." 

"We agreed that the massacre has to stop, that oppression should end and that regional stability should be preserved."

The EU Council President stressed that Egypt is "a key country in a region which is so close and important for Europe." "Egypt's success will have positive repercussions on the region as a whole," he added.

Earlier, Barroso said: "We are also adamant that Assad should go.We need a transition to an inclusive democracy."

Morsi interrupted to add that this was "completely agreed upon."

According to an Egyptian journalist present at the press point, Morsi, who spoke in Arabic, repeated his commitment "to respect Egypt’s international accords" including the peace treaty with Israel.