Washington warned against travel to Egypt after an American was among three people killed during rival demonstrations for and against Islamist President Mohamed Morsi ahead of Sunday's anniversary of his turbulent maiden year in office, AFP reports.
The US State Department also authorised the departure of non-essential embassy staff for fear of further deadly violence in the face of the bitter antagonism between Morsi's Islamist supporters and the mainly secular opposition.
Morsi's opponents have called nationwide protests for Sunday to demand that he step down, sparking counter-demonstrations by the Muslim Brotherhood and its Islamist allies that have triggered often bloody clashes.
The US citizen was killed as he took photographs of a demonstration in the Mediterranean coastal city of Alexandria, Egyptian officials said.
"We can confirm that a US citizen was killed in Alexandria, Egypt," State Department spokesman Patrick Ventrell said in a statement.
A statement posted on the website of Kenyon College in Ohio, said US embassy officials had identified him as one of their students, Andrew Pochter, 21, from Maryland.
He had been working as an intern at AMIDEAST, an American non-profit organisation, the statement added.
Another man was killed earlier during the clashes in Alexandria.
In the canal city of Port Said, an Egyptian journalist was killed and several other people injured after someone threw a small explosive device at anti-Morsi protesters, a security official and witnesses said.
Clashes also erupted in the Nile Delta provinces of Daqahliya and Beheira. Across the country more than 130 people were wounded, security officials said.
The offices of the Freedom and Justice Party (FJP), the political arm of the Muslim Brotherhood, were torched in Alexandria and at Aga in Daqahliya, and its offices were stormed in Beheira.
The skirmishes are seen as a prelude to the mass anti-Morsi protests planned for Sunday, the anniversary of his taking office as Egypt's first freely elected president.
Morsi, 62, has been accused by opponents of failing the 2011 revolution that brought him to power and of ignoring nearly half of the electorate of around 50 million who did not vote for him last year.
Sunday's protest has been called by Tamarod (Arabic for Rebellion), a grassroots movement which says it has more than 15 million signatures for a petition demanding Morsi's resignation and a snap election.
Friday's pro-Morsi demonstrations were seen as a preemptive strike by the president's supporters against what they see as an attempt to subvert Egypt's fledgling democracy.
"We will not allow a coup against the president," senior Brotherhood leader Mohamed al-Beltagui told tens of thousands of Morsi supporters who rallied in the capital.
Anti-Morsi protesters joined hundreds camped overnight in Cairo's iconic Tahrir Square, epicentre of the 2011 revolt that toppled Hosni Mubarak and catapulted the Islamist to the presidency.
Opponents also gathered in Alexandria, Mansura and Port Said.
"It's not about sacking Morsi himself," one Tahrir protester told AFP.
"If any other does the same he will be sacked as well. Our demands are clear: bread, freedom, social justice and human dignity."
Washington called for calm.
"We urge all parties to refrain from violence and express their views peacefully," US State Department spokesman Patrick Ventrell said.
"And political leaders have the responsibility of taking steps to ensure that groups do not resort to violence."
Morsi warned in a televised speech on Wednesday that the growing polarisation threatened to "paralyse" Egypt, and appealed to the opposition to join talks.
On Thursday however, the opposition National Salvation Front coalition rejected his offer and renewed its call for a snap presidential election.
The State Department warned Americans "to defer non-essential travel to Egypt at this time due to the continuing possibility of political and social unrest."
"US citizens are urged to remain alert to local security developments and to be vigilant regarding their personal security," it added in an updated travel warning.
Malaysia too warned its nationals to postpone travel to Egypt.
Germany warned that Egypt's fledgling democracy faced a "moment of truth", and urged Morsi to implement reforms.
Amnesty International called on the authorities to ensure the security forces showed restraint and protected peaceful demonstrators from violence over the weekend.
"They should make clear that anyone responsible for arbitrary and abusive force will be brought to justice," Hassiba Hadj Sahraoui, Amnesty's Middle East deputy director said in a statement.
At least four other people have died since Wednesday in clashes in the Nile Delta -- three in Mansura city and one in Zagazig, medics said.
Egypt is deeply split between Morsi's Islamist allies and an opposition of leftists, liberals, Christians and some Muslim groups.
The army, which oversaw the transition from Mubarak's autocratic rule but has been on the sidelines since Morsi's election, has warned it would intervene in the event of violence.