The State Department issued a new travel warning Thursday afternoon calling on U.S. citizens to leave Egypt as soon as possible because of the military’s bloody crackdown in the country that has taken the lives of 638 people.

Americans who choose to stay should avoid all demonstrations in Egypt, the State Department said, “as even peaceful ones can quickly become violent, and a foreigner could become a target of harassment or worse.”

The U.S. embassy near Tahrir Square in Cairo was closed to the public Thursday after the Egyptian government Wednesday declared a nationwide state of emergency and imposed night-time curfews. Supporters of deposed Islamic President Mohammed Morsi torched two local government buildings near the capital Wednesday, and the Egyptian military responded by killing more than 500 Morsi supporters holding sit-ins.

At the same time, attacks on Coptic Christian churches continued for a second day, according to Egypt’s official news agency. The warning also noted that a U.S. citizen was killed in late June during a demonstration in Alexandria.

Earlier Thursday President Obama took time out from his Martha’s Vineyard vacation to make a public statement, urging restraint on both sides and announcing the cancellation of upcoming joint military exercises in response to the violence. He said the interim government should respect the rights of protesters to demonstrate peacefully and urged protesters to avoid violence.

U.S. Defense Secretary Chuck Hagel Thursday afternoon called Egyptian defense chief Gen. Abdel Fattah al Sisi and pledged to “maintain a military relationship with Egypt,” according to a Pentagon statement.

“But I made clear that the violence and inadequate steps towards reconciliation are putting important elements of our longstanding defense cooperation at risk,” Hagel stressed.