One person was killed in Cairo as clashes erupted between supporters and opponents of Egypt's ousted president Mohamed Morsi, as tensions mounted ahead of a looming crackdown on pro-Morsi protest camps.
At least 10 people were also injured in the violence in Cairo's Giza neighbourhood, security officials told AFP on Tuesday.
A pro-Morsi march had taken off from Nahda square -- site of one of two large sit-ins staged by Morsi loyalists -- to Faisal Street in Giza where residents began to pelt the marchers with rocks.
The clashes rapidly escalated with birdshot fired from both sides, security officials said, as residents of the Giza neighbourhood smashed the shopfront of a department store owned by Islamists.
Earlier in another area of the capital, police fired tear gas to break up clashes that erupted between Morsi loyalists and residents, AFP correspondents reported.
Dozens of religious scholars affiliated with Morsi's Muslim Brotherhood had entered the religious endowments ministry and were ordered out by police prompting clashes, a security official said.
The United States urged the military-backed interim government to allow Morsi supporters to protest freely.
State Department deputy spokeswoman Marie Harf said Washington regarded freedom to protest as a "key part" of the democratic process but would be concerned by reports of violence.
"Clearly, we're watching the situation on the ground very closely," Harf said.
"We encourage the interim government to allow people to protest -- that's a key part of moving forward with the democratic process, and of course, would be concerned by new reports of violence."
The United States, which provides $1.5 billion in mostly military aid to Egypt every year, maintains close ties to the Egyptian military but says it favors a rapid return to elected civilian rule.
The violence comes after the expiry of a government ultimatum to dismantle the sprawling protest camps.
Morsi, Egypt's first elected president, was overthrown by the military on July 3 with popular backing.
His supporters say nothing short of his reinstatement will persuade them to disperse.
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The standoff with the army-backed interim government has sparked international fears of further bloodshed.
Clashes between pro- and anti-Morsi demonstrators and security forces have killed more than 250 people since the end of June.
Since police issued the latest warning last week to end the protests, the Islamists have repeatedly called for new demonstrations.
On Monday, the judiciary extended Morsi's detention for a further 15 days pending an investigation into his collaboration with Palestinian group Hamas.
Morsi's backers set as their rallying cry: "Together against the coup d'etat and the Zionists", in an appeal to nationalist sentiment after a deadly air strike on militants in Egypt's Sinai Peninsula, which the jihadists said was carried out by an Israeli drone.
Israeli media say the Jewish state has been cooperating closely with Egypt over the threat from Sinai militants.
Authorities have announced plans to clear the pro-Morsi protest camps from Cairo's Rabaa al-Adawiya and Nahda squares by "gradual steps".
But the number of protesters in the squares has not diminished.
At Rabaa, the bigger of the two rallies, dozens of volunteer guards manned makeshift barriers of bricks and sandbags.
The Muslim Brotherhood, the group from which Morsi hails, insist that their demonstrations are peaceful, while the government and the press accuse demonstrators at Rabaa and Nahda of being "terrorists".
They say the protesters are hiding automatic weapons in the squares and using women and children as "human shields".
The government has struggled to come up with a clear strategy to end the protests, its members split between those who want to send in the security forces and those who want a negotiated solution, in deference to international appeals to avoid further bloodshed.
Police and army chiefs are ready to intervene, but the reticence of some top politicians, such as vice-president and Nobel laureate Mohamed ElBaradei, has led them to take a more cautious approach.
The Muslim Brotherhood, banned in 1954 and repressed by successive governments, won both parliamentary and presidential elections in 2011 after the ouster of veteran strongman Hosni Mubarak.
The Brotherhood is demanding the release of Morsi and other top party figures who were detained by the military on July 3.
Prosecutors have set an August 25 date for the trial of the Brotherhood Supreme Guide Mohammed Badie and his two deputies.