An American and an Egyptian journalist have been killed in Egypt in clashes between protesters opposed to President Mohamed Morsi and those backing him.
The rival demonstrations involving tens of thousands of people began on Friday in the northern port city of Alexandria, ahead of a mass opposition rally planned for Sunday, which marks the end of the first year of Morsi's four-year term.
Reuters news agency said a third man was killed and 10 injured in an explosion during a protest in Port Said, at the mouth of the Suez Canal.
Tensions are rising ahead of Sunday's rally.
Andrew Pochter, a 21-year-old who worked for an American cultural centre in the coastal city of Alexandria, was killed on Friday as he took photographs of the demonstration, officials said.
He was reported to have been working in Egypt teaching English to children and trying to improve his Arabic language skills.
The State Department has authorised the departure of non-essential embassy staff in Egypt, and their family members.
In an updated travel warning, the department cautioned US citizens "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," said the travel advisory.
Britain also updated its travel advice for Egypt, urging citizens against "all but essential" travel to the country.
In the canal city of Port Said, an Egyptian journalist was killed and several others injured after a small explosive device was thrown at anti-Morsi protesters, a security official and witnesses said.
Clashes also erupted in the Nile Delta provinces of Daqahliya and Beheira, and across the country over 130 people were wounded, security officials said.
More violence expected
A senior scholar from Al-Azhar, Egypt's highest Sunni religious authority, warned of worsening violence in the run up to Sunday, which he blamed on "criminal gangs".
"Vigilance is required to ensure we do not slide into civil war," said Hassan el-Shafei, in remarks carried by state media.
Protests on Sunday, which organisers hope will draw millions of Egyptians to the streets, will demand that Morsi resign and cede power to a transitional government.
The rally on Friday was intended as a preemptive strike, a chance for organisers to show that Morsi still commands majority support.
"Don't believe that everyone is against the president," said Naeem Ghanem, carrying banners accusing the opposition of working with the United States and Israel. "Ninety percent of the people are with Morsi."
The rally was dubbed "legitimacy is a red line", and demonstrators kept returning to that theme, arguing that the only way to remove the democratically-elected president is through the ballot box.
"I'm here to defend my voice. If you want Morsi to leave, that's fine, but after four years," said Taher Mohamed, manning a stall and selling pro-Morsi gear at the rally.
Amnesty International called on 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 on Friday.
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.