Egyptian President Mohamed Morsi said he had cut all diplomatic ties with Damascus on Saturday and backed a no-fly zone over Syria, pitching the most populous Arab state more firmly against President Bashar al-Assad.
Addressing a rally called by Sunni Muslim clerics in Cairo, the Sunni Islamist head of state also warned Assad's ally, the Iranian-backed Lebanese Shi'ite militia Hezbollah, to pull back from fighting in Syria.
"Hezbollah must leave Syria. These are serious words," said Morsi, whose country hosted a conference of Sunni clerics this week who issued a call for holy war against Damascus. "There is no space or place for Hezbollah in Syria."
The rally underscored the region's deepening sectarian rift. A cleric who spoke before Morsi described Shi'ites as heretics, infidels, oppressors and polytheists.
It was also a show of support for Morsi as his opponents mobilize for protests to demand early presidential elections.
Morsi waved Syrian and Egyptian flags as he entered the auditorium packed with 20,000 supporters. The crowd chanted: "From the free revolutionaries of Egypt: We will stamp on you, Bashar!"
Morsi, a Muslim Brotherhood politician, steered clear of direct references to Shi'ites and Iran but in a partial allusion to Tehran, he accused states in the region and beyond of feeding "a campaign of extermination and planned ethnic cleansing" in Syria.
"We decided today to entirely break off relations with Syria and with the current Syrian regime," he said. He also urged world powers not to hesitate to enforce a no-fly zone over Syria.
Western diplomats said on Friday that Washington was considering a limited no-fly zone over parts of Syria, but the White House said later that the United States had no national interest in pursuing that option.
Russia, an ally of Assad and fierce opponent of outside military intervention in Syria, said any attempt to impose a no-fly zone using F-16 fighter jets and Patriots based in Jordan would be illegal.
Morsi said he was organizing an urgent summit of Arab and other Islamic states to discuss the situation in Syria, where the United States has in recent days decided to take steps to arm the rebels.
Egypt's U.S.-funded and -trained army is among the most powerful in the Middle East. There has been no suggestion, however, that Egypt, a country steeped in poverty, should get involved in the fighting in Syria.
Warns Against Violence
Morsi said: "The Egyptian people supports the struggle of the Syrian people, materially and morally, and Egypt, its nation, leadership ... and army, will not abandon the Syrian people until it achieves its rights and dignity."
The Brotherhood has joined calls this week from Sunni Muslim religious organizations for jihad against Assad and his Shi'ite allies.
Egypt has not taken an active role in arming the Syrian rebels, but an aide to Morsi said this week that Cairo would not stand in the way of Egyptians who wanted to fight in Syria.
It marked Morsi's second combative foreign policy speech in less than a week. On Monday, he said Egypt would keep "all options open" for dealing with a dispute with Ethiopia over a giant dam it is building on the Nile, though he said Cairo did not want war and stressed it would work diplomatically.
Morsi's liberal and leftist opponents are mobilizing for mass protests on June 30, the anniversary of Morsi coming to office, fuelling fears of possible further violence.
Morsi told his Islamist supporters at the rally that they must not be dragged into confrontations and that he would not tolerate any violence.