Egypt's interim leader vowed fresh elections by early next year after 51 people, mostly supporters of ousted president Mohammed Morsi, were killed outside Cairo military barracks Monday.

Morsi's Muslim Brotherhood, which has led demonstrations against Wednesday's military overthrow of the Islamist leader, called for an "uprising," saying troops and police "massacred" its supporters during dawn prayers in Cairo Monday.

The United States on Monday called for "maximum restraint" from Egypt's military and condemned the Muslim Brotherhood's calls for an uprising after some 50 people were shot dead at a demonstration.

The White House also said there would be no immediate cutoff in aid to Egypt following the military's ouster of Islamist president Mohammed Morsi, Egypt's first democratically elected leader.

EU foreign policy chief Catherine Ashton on Monday warned all sides in Egypt against "provocation or escalation" as Islamists called for an uprising after the deaths of dozens of loyalists of the country's ousted president.

A spokesperson for Ashton said in a statement that she urged all sides "to move rapidly toward reconciliation" and that "all those who claim legitimacy must ... avoid any provocation or escalation of violence".

Germany called for an independent inquiry into the killing of 42 loyalists of Egypt's ousted president Monday, saying it feared political violence in the country could continue to spiral.

Expressing "shock" about the reports of demonstrators killed while protesting last week's military coup in Cairo, the foreign ministry in Berlin said that all sides must now refrain from bloodshed.

Thousands of people protested in the Yemeni capital on Monday against the Egypt military's ouster of Islamist president Mohammed Morsi, the country's first elected leader in decades.

"We are with legitimacy," read a banner carried by the protesters who marched towards Cairo's embassy in Sanaa, waving Egyptian flags.

Jordan's Muslim Brotherhood on Monday condemned the "massacre" of 51 loyalists of Egypt's ousted Islamist president Mohammed Morsi and urged more demonstrations to restore him.

"We strongly condemn the massacre committed by the neo coupists that has clearly showed the truth about the bloody military coup," the Islamic Action Front (IAF), the political arm of the Muslim Brotherhood, said on its website.

Fifty-one loyalists of Egypt's ousted president were killed Monday while demonstrating against last week's military coup, triggering an Islamist uprising call as the army urged an "end of the sit-in."

The Muslim Brotherhood, which has led demonstrations against Wednesday's overthrow of Islamist president Mohammed Morsi, said its supporters were "massacred" by troops and police during dawn prayers in Cairo.

About 200 Sudanese Islamists demonstrated peacefully outside Egypt's embassy in Khartoum on Monday to support ousted Egyptian president Mohammed Morsi, an Agence France Presse photographer said.

"We are with the legal president of Egypt," read a banner carried by the group, which also waved Egyptian flags.

Sunni Islam's leading cleric, Ahmed al-Tayyeb, said on Monday he will retire into seclusion until the end of violence in Egypt, after bloody clashes that left 42 people dead.

Tayyeb, who heads the Cairo-based Al-Azhar -- Sunni Islam's highest seat of learning -- said he would "remain in seclusion in his house until all the spilling of Egyptian blood ends and those behind it take responsibility".

Gas-rich Qatar, a key backer of the Muslim Brotherhood to which Egypt's Mohammed Morsi belongs, condemned the killing of 42 loyalists of the ousted president on Monday, and called on all Egyptians to abandon violence.

The Muslim Brotherhood, which has led demonstrations against last Wednesday's overthrow of Morsi, said its supporters were "massacred" when police and troops fired on them during dawn prayers outside an elite army headquarters in Cairo.