Four protesters were killed when a mob stormed the grounds of the U.S. embassy in Yemen Thursday, part of a wave of violent demonstrations against an anti-Islam film produced in the United States.

Yemeni President Abed Rabbo Mansour Hadi immediately condemned the violence and promised to protect U.S. citizens in Yemen. The White House says President Barack Obama telephoned Mr. Hadi to thank him for his swift response. It says Mr. Obama rejects any efforts to denigrate Islam, but said there is no justification for the violence.

Protesters also marched in Cairo, Tehran, Baghdad and Dhaka, chanting “no to Israel” and burning the American flag.

U.S. Secretary of State Hillary Clinton condemned the amateur U.S.-made movie that mocks the Islamic Prophet Muhammad. She called it “disgusting” and “reprehensible.” Egyptian President Mohamed Morsi also condemned both the film and the violence Thursday. He promised to protect foreigners in Egypt.

U.S. and Libyan authorities are investigating Tuesday's storming of the U.S consulate in Benghazi that killed U.S. Ambassador Christopher Stevens and three of his staff. One of those killed was identified Thursday as a former U.S. Navy SEAL who was on a security detail in Libya.

American intelligence agencies are examining the alleged involvement of pro-al Qaida militants. But they say they do not have solid evidence.

The United States also has sent two Navy destroyers, a Marine Corps anti-terrorist security team and agents from the Federal Bureau of Investigation to Libya to protect Americans.