Protest in Cairo
Protesters gather as they chant anti-President Mohamed Mursi slogans during a protest in Tahrir square in Cairo on June 28, 2013. Reuters

The U.S. issued a travel advisory on Friday, warning its citizens against traveling to Egypt, and instructed non-emergency U.S. diplomatic staff to leave the country, after an American was killed in the Mediterranean coastal city of Alexandria in clashes between supporters and opponents of Egypt’s President Mohamed Morsi.

Egypt’s opposition has planned nationwide protests demanding Morsi’s resignation on Sunday, the day he completes a year as president.

The State Department warned U.S. citizens “to defer non-essential travel to Egypt at this time due to the continuing possibility of political and social unrest.”

“On May 9, a private U.S. citizen was attacked with a knife outside of the Embassy after being asked whether he was an American. Additionally, Westerners and U.S. citizens have occasionally been caught in the middle of clashes and demonstrations,” the state department said.

“Political unrest, which intensified prior to the constitutional referendum in December 2012 and the anniversary in 2013 of Egypt's 25th January Revolution, is likely to continue in the near future due to unrest focused on the first anniversary of the president’s assumption of office.”

The Cairo International Airport saw an exodus of departing passengers, which airport officials described as “unprecedented,” Associated Press reported. All flights on Friday bound to Europe, the U.S. and the Middle East were fully booked, the report said, citing officials.

In Cairo, tens of thousands of supporters and opponents of Morsi thronged the streets on Friday, while in Alexandria, clashes erupted between the opposing sides, killing two people, including the American.

Gen. Amin Ezz Eddin, Alexandria’s security chief, told Al-Jazeera that the American was killed in Sidi Gabr Square while photographing the clashes.

A State Department official confirmed the killing to NBC News, and added that the U.S. was “providing appropriate consular assistance from our Embassy in Cairo and our Bureau of Consular Affairs at the State Department. We do not have further information to provide at this time.”

The State Department did not identify the individual, but Kenyon College in Gambier, Ohio, issued a statement saying one of its students, Andrew Pochter, 21, of Chevy Chase, Md., was killed in Alexandria on Friday.

“Pochter was an intern at AMIDEAST, an American non-profit organization engaged in international education, training and development activities in the Middle East and North Africa,” the statement said. “The AMIDEAST internship is not a Kenyon program. An appreciation of Pochter's life will be shared at a later time.”

Six people have been killed in nationwide clashes this week, including Friday’s death, according to AP.

“We must be alert lest we slide into a civil war that does not differentiate between supporters and opponents,” Sheik Hassan al-Shafie, a senior cleric at Al-Azhar, the country’s top Muslim religious institution, was quoted as saying by AP.