Islamists fought protesters outside the Egyptian president's palace on Wednesday, while inside the building his deputy proposed a way to end a crisis over a draft constitution that has split the most populous Arab nation.
Stones and petrol bombs flew between opposition protesters and supporters of President Mohamed Mursi who had flocked to the palace in response to a call from the Muslim Brotherhood.
Two Islamists were hit in the legs by what their friends said were bullets fired during the clashes in streets around the compound in northern Cairo. One of them was bleeding heavily.
A leftist group said Islamists had cut the ear off one of its members, inflicting serious head wounds on him.
Riot police began to deploy between the two sides to try to end the violence which flared after dark despite an attempt by Vice President Mahmoud Mekky to calm the political crisis.
He said amendments to disputed articles in the draft constitution could be agreed with the opposition. A written agreement could then be submitted to the next parliament, to be elected after a referendum on the constitution on December 15.
"There must be consensus," he told a news conference, saying opposition demands must be respected to overcome the crisis.
Opposition leader Amr Moussa, a former foreign minister and secretary-general of the Arab League, said Mursi should make a formal offer for dialogue if his opponents were to consider seriously Mekky's ideas for a way out of the political impasse.
"We are ready when there is something formal, something expressed in definite terms, we will not ignore it," Moussa told Reuters during talks with other opposition figures.
Opposition leaders have previously urged Mursi to retract a decree widening his powers, defer the plebiscite and agree to revise the constitution, but have not echoed calls from street protesters for his overthrow and the "downfall of the regime".
Mursi had returned to work at his compound a day after it came under siege from protesters furious at his assumption of extraordinary powers via an edict on November 22.
The president, narrowly elected by popular vote in June, said he acted to stop courts still full of judges appointed by ousted strongman Hosni Mubarak from derailing a constitution meant to complete a political transition in Egypt, long an ally of Washington and signatory to a 1979 peace deal with Israel.
Rival groups skirmished earlier outside the presidential palace on Wednesday. Islamist supporters of Mursi tore down tents erected by leftist foes, who had begun a sit-in there.
"They hit us and destroyed our tents. Are you happy, Mursi? Aren't we Egyptians too?" asked protester Haitham Ahmed.
Mohamed Mohy, a pro-Mursi demonstrator who was filming the scene, said: "We are here to support our president and his decisions and save our country from traitors and agents."
Facing the gravest crisis of his six-month-old tenure, Mursi has shown no sign of buckling, confident that Islamists can win the referendum and a parliamentary election to follow.
Many Egyptians yearn for an end to political upheaval that has scared off investors and tourists, damaging the economy.
Mekky said street mobilization by both sides posed a "real danger" to Egypt. "If we do not put a stop to this phenomenon right away ... where are we headed? We must calm down."
U.S. Secretary of State Hillary Clinton weighed into Egypt's political debate, saying dialogue was urgently needed on the new constitution, which should "respect the rights of all citizens".
Clinton and Mursi worked together last month to broker a truce between Israel and Hamas Islamists in the Gaza Strip.
"It needs to be a two-way dialogue ... among Egyptians themselves about the constitutional process and the substance of the constitution," Clinton told a news conference in Brussels.
Washington is worried about rising Islamist power in Egypt, a staunch U.S. security partner under Mubarak.
The Muslim Brotherhood had summoned supporters to an open-ended demonstration at the presidential palace, a day after about 10,000 opposition protesters had encircled it for what organizers dubbed a "last warning" to Mursi.
"The people want the downfall of the regime," they chanted, roaring the signature slogan of last year's anti-Mubarak revolt.
Officials said 35 protesters and 40 police were wounded.
The "last warning" may turn out to be one of the last gasps for a disparate opposition that has little chance of scuttling next week's vote on a constitution drawn up over six months and swiftly approved by an Islamist-dominated assembly.
State institutions, with the partial exception of the judiciary, have mostly fallen in behind Mursi.
The army, the muscle behind all previous Egyptian presidents in the republic's six-decade history, has gone back to barracks, having apparently lost its appetite to intervene in politics.
In a bold move, Mursi sacked Mohamed Hussein Tantawi, the Mubarak-era army commander and defense minister, in August and removed the sweeping powers that the military council, which took over after Mubarak fell, had grabbed two months earlier.
The liberals, leftists, Christians, ex-Mubarak followers and others opposed to Mursi have yet to generate a mass movement or a grassroots political base to challenge the Brotherhood.
Investors have seized on hopes that Egypt's turbulent transition, which has buffeted the economy for two years, may soon head for calmer waters, sending stocks 1.6 percent higher after a 3.5 percent rally on Tuesday.
Egypt has turned to the IMF for a $4.8 billion loan to help it out of a crisis that has depleted its foreign currency reserves. The government said on Wednesday the process was on track and its request would go to the IMF board as expected.
The board is due to review the facility on December 19.