THE killing of the U.S. ambassador to Libya and three other Americans on Tuesday sparked a security crisis in the North African country, elevated tensions across the Middle East and raised concerns about how well the United States can protect its diplomats abroad. The United States responded to the assault by dispatching two navy destroyers, dozens of Marines, federal investigators and intelligence assets to Libya to protect Americans and help hunt the suspected religious extremists who carried out the attack late Tuesday. U.S. officials described the attack that killed Ambassador Christopher Stevens as complex and possibly premeditated. The assault in the Libyan city of Benghazi, along with a protest at the American Embassy in Cairo, fueled a harsh exchange between U.S. President Barack Obama and Republican nominee Mitt Romney. Obama said the United States will work with Libya to bring the attackers to justice. He and other officials didn’t rule out a U.S. strike. “Make no mistake, justice will be done,’’ the president said. Secretary of State Hillary Clinton said the attack should “shock the conscience” of people of all faiths, but wouldn’t alter U.S. policy in Libya. The United States also announced increased security measures for all U.S. diplomatic facilities. Libyan officials, many of whom led the rebel government based in Benghazi and worked with Stevens during that time, condemned the killings. The head of the new congress, Mohammed Magarief, apologized to the American public for the tragedy. By late Wednesday, no one had been arrested. Officials in Tripoli were scrambling to implement a response to what they admitted was a monumental security breach. Egyptian protesters climbed the walls of the U.S. Embassy in Cairo and replaced the flag with a black standard bearing an Islamic inscription, in protest of a film deemed offensive to the Prophet Muhammad. The United States sent the destroyers U.S.S. Laboon and U.S.S. McFaul to the Libyan coast to aid in any evacuations or humanitarian missions, said a U.S. official. A U.S. Marine team was sent to supplement security at the U.S. Embassy in Tripoli, arriving there Wednesday. The unit is known as a Fleet Antiterrorism Security Team, or FAST team. These typically number 50 Marines. (SD-Agencies) ? | 