Supporters of Egypt's ousted president called for new protests on Monday, threatening to deepen the country's crisis as the EU foreign policy chief met both the government and the opposition.

The Anti-Coup Alliance of Islamist groups organizing protests against the ouster of president Mohammed Morsi urged demonstrators to march on security buildings on Monday night and called a million-man march for Tuesday.

EU foreign policy chief Catherine Ashton headed to Egypt on Sunday, as the country's political crisis deepened with a deadlock between the interim government and supporters of the ousted president.

Ashton's visit, confirmed by Egypt's vice presidency, comes a day after 72 people were killed at a protest in support of deposed Islamist leader Mohammed Morsi.

Egypt's presidency said Sunday it was "saddened" by the deaths of 72 people at a protest in support of ousted Islamist president Mohammed Morsi, but linked the bloodshed to "terrorism".

"We are saddened by the spilling of blood on the 27th," Mostafa Hegazy, an adviser to army-backed interim president Adly Mansour, told reporters.

Egyptian security forces killed 10 "terrorist" gunmen and captured 20 in an operation in the Sinai Peninsula over the past 48 hours, state news agency MENA reported on Sunday.

"Security operations carried out by the armed forces and police in north Sinai to hunt down armed terrorists... (resulted) in the liquidation of 10 of these armed terrorist elements," the agency said, citing a security source.

At least 15 people were injured in the Egyptian city of Port Said overnight in clashes involving supporters of ousted President Mohammed Morsi, state news agency MENA reported.

Witnesses and MENA said Morsi supporters had opened fire during the funeral of a fellow loyalist, but the ousted president's Muslim Brotherhood group denied the claims.

Human Rights Watch on Sunday condemned the deaths of more than 70 people in violence that erupted at protests in Egypt, accusing authorities of a "criminal disregard for people's lives".

At least 72 people were killed in Cairo alone on Saturday morning, according to the Health Ministry, at a rally of supporters of ousted Islamist President Mohammed Morsi.

At least 72 people were killed during clashes in Cairo on Saturday, Egypt's Health Ministry said, after violence erupted at a demonstration in support of ousted President Mohammed Morsi.

The ministry said nine others had died in violence in Egypt's second city, Alexandria, a day earlier, putting the toll in two days of unrest at 81.

At least 74 supporters of Egypt's ousted Islamist president were shot dead during clashes with security forces, officials said Saturday, as rival rallies were staged for and against Mohammed Morsi

In the heaviest bloodshed since Morsi's July 3 overthrow, Ahmad Aref, spokesman of Morsi's Muslim Brotherhood, said 66 people died in the violence and another 61 were left "clinically dead."

The sheikh of al-Azhar, Sunni Islam's top authority, condemned Saturday the deaths of dozens of supporters of Egypt's ousted president Mohamed Morsi and called for an inquiry as Vice President Mohammed ElBaradei condemned what he called the “excessive use of force.”

"The sheikh of Al-Azhar deplores and condemns the deaths of a number of martyrs who were victims of today's events," Ahmed al-Tayyeb, who heads the Cairo-based al-Azhar, said in a statement.

British Foreign Secretary William Hague on Saturday condemned the use of force against protesters during deadly clashes in Cairo and accused Egyptian security forces of using live rounds.

Hague also called on Egyptian authorities to either release or charge all political leaders detained since the army toppled Islamist president Mohamed Morsi on July 3. Morsi himself remains in detention.