Three people have been killed in Alexandria, Egypt, during clashes in the city between President Mohamed Morsi's supporters and opponents. Fighting in other parts of the country has also resulted in dozens of injuries.
Three people were killed in Alexandria and 85 injured as Morsi protesters set Muslim Brotherhood offices alight, officials said.
The US State Department confirmed 21-year-old university student Andrew Pochter was killed while photographing the protests.
A fourth man was killed and 10 injured in an explosion during a protest in Port Said. Authorities were not certain about the cause of the blast, but Morsi protesters heard it and assumed it was an explosion and responded accordingly with protest.
Tensions have also been simmering elsewhere in Egypt. In Cairo, for example, thousands of Morsi supporters gathered near a big mosque to defend the president's legitimacy. In the center of the city's Tahrir Square, meanwhile, opponents carried flags and chanted "Leave!"
Clashes in the Delta province of Aga have also resulted in dozens of injuries.
Including Friday's victims, a total of six have been killed this week.
The US State Department reacted to the violence on Friday by warning Americans against nonessential travel to Egypt. Nonessential staff and families of US embassy personnel in Cairo are being allowed to leave the country until conditions improve.
The rising tensions signal a deepening resentment of the ruling Islamists by the predominately secular opposition, and many now fear that the political divide in Egypt will become more polarized and lead to more widespread violence.
Even Egypt's leaders are voicing concern over the security situation. Egypt's leading religious authority, for example, urged Egyptians on Friday to remain calm, warning that such violence could lead to "civil war."
"Vigilance is required to ensure we do not slide into civil war," said clerics at Cairo's Al-Azhar institute, an influential center of Muslim scholarship.
Opponents of Morsi, Egypt's first democratically elected president, accuse the Islamist leader of failing to fulfill the objectives of the revolution that unseated president Hosni Mubarak over two years ago.
They also blame the ruling Muslim Brotherhood for failing to address the nation's economic and social woes while consolidating its own power.
Supporters of Morsi, meanwhile, want to see him complete his full four-year term, staying in power through 2016.
tm/ccp (AP, AFP, dpa, Reuters)