Updated

The choice of Nobel Peace laureate Mohamed ElBaradei as Egypt's interim premier ran into opposition within the coalition that backed Mohamed Morsi's overthrow, as supporters and opponents of the ousted Islamist president planned rival rallies Sunday.

The official MENA news agency had reported on Saturday that caretaker president Adly Mansour had appointed the outspoken liberal opponent of Morsi, only for his office to later deny any final decision had been taken.

Reporters had already assembled at the presidential palace for promised statements from Mansour and ElBaradei which were then abruptly called off.

Salafi Islamists, who gave their backing to Morsi's overthrow in a military coup on Wednesday, were holding out against ElBaradei's appointment, arguing that he was a divisive choice, a source close to the discussions told AFP.

Mansour adviser, Ahmed al-Muslimani, said ElBaradei, the former head of the UN nuclear watchdog, remained the "strongest candidate." "He is on top of the list of names," Muslimani told AFP.

The Mansour aide held out an olive branch to Morsi supporters in the Muslim Brotherhood as its leaders vowed to press protests rejecting his ouster.

"We extend our hand to the Muslim Brotherhood," Muslimani told a press conference.

"I think the Muslim Brotherhood has many opportunities in the coming period, to enter elections."

The initial reports of ElBaradei's appointment had been greeted with cheers in Cairo's Tahrir Square and Ittihadiya presidential palace, where opponents of Morsi set off firecrackers, frantically waved Egyptian flags and honked car horns.

The celebrations came as the Muslim Brotherhood staged a new show of force to demand the military restore Morsi to power, after 24 hours of violence that left 37 people dead and over 1,400 injured.

Tamarod, the grassroots movement which organised the mass protests against Morsi that prompted the army to intervene, called for new demonstrations on Sunday to counter the Islamists, sparking fears of clashes.

Thousands of Morsi supporters on Saturday mourned four Brotherhood members killed during protests against Morsi's ouster.

The imam told the tearful crowd gathered outside Cairo's Rabaa al-Adawiya mosque to pray for the "martyrs of legitimacy".

Morsi, who has been in detention since overnight on Wednesday, had issued a defiant call for his supporters to defend his "legitimacy" as Egypt's first freely elected president, in a pre-recorded speech posted shortly after his ouster.

Influential Egyptian-born Islamist cleric Yusuf al-Qaradawi, issued a fatwa, or religious ruling from his base in Qatar urging Egyptians to support Morsi.

Friday's violence erupted despite talk of peaceful protests.

Residents of one Cairo district reported that bearded Islamists armed with machineguns, machetes and sticks clashed with them as they passed through their district overnight.

"The Brotherhood attacked the area with all kinds of weapons," said Mohammed Yehya, who said he lost three friends in the mayhem.

In response, a spokesman for the Brotherhood's Freedom and Justice Party told AFP: "Not everyone with a beard belongs to the Muslim Brotherhood."

The bloodletting continued on Saturday with gunmen killing a Coptic Christian priest in the Sinai Peninsula.

Militants in the Sinai also blew up a gas pipeline to Jordan, for the first time in nearly a year, as soldiers and police came under attack by Islamist gunmen.

On Friday, armed Morsi supporters stormed the North Sinai provincial headquarters in the town of El-Arish and raised the black banner of Al-Qaeda-inspired militants, an AFP correspondent reported.

Morsi's single year of turbulent rule was marked by accusations he failed the 2011 revolution by concentrating power in Brotherhood hands and letting the economy nosedive.

President Barack Obama meanwhile insisted the United States was "not aligned" with any political party or group in Egypt following Morsi's ouster.

Obama, who spoke with members of the National Security Council by conference call, "condemned the ongoing violence across Egypt and expressed concern over the continued political polarisation," according to a White House statement.

"The United States categorically rejects the false claims propagated by some in Egypt that we are working with specific political parties or movements to dictate how Egypt's transition should proceed," the statement said.

"The future path of Egypt can only be determined by the Egyptian people."

Washington also echoed calls by UN chief Ban Ki-moon for a peaceful end to the crisis.

But Republican Senator John McCain called for a suspension of US military aid to Cairo because the army had "overturned the vote of the people".