BERLIN -- U.S. embassies across the world ramped up security Thursday following an attack that killed the U.S. ambassador to Libya, as Muslims angry over an anti-Islam film stormed the U.S. mission in Yemen and clashed with police near the American mission in Cairo.
President Barack Obama ordered increased security at U.S. sites worldwide after Ambassador Chris Stevens and three other Americans were killed Tuesday in an attack on the U.S. Consulate in Benghazi, Libya.
The Benghazi attack followed the storming of the U.S. Embassy in Cairo after the trailer from an American-made film, "Innocence of Islam," went viral on YouTube. Libyan officials said militants used civilians protesting the film as cover for a violent assault timed for the 11th anniversary of the Sept. 11, 2001, attacks.
As violence continued Thursday, embassies from the Philippines to the Middle East warned Americans to be on guard for more protests, especially on Friday, the main Muslim day of prayer when religious fervor runs high.
In Yemen, hundreds of protesters chanting "Death to America!" stormed the U.S. Embassy compound in the capital, Sanaa, and burned the American flag. Yemen's president, Abed Rabbo Mansour Hadi, quickly apologized to the U.S. for the attack and vowed track down the culprits.
In Dhaka, Bangladesh, police stopped a march by about 400 people who burned a U.S. flag several miles from the U.S. Embassy, where higher security was evident. And in Cairo, where protests against the film began, police fired tear gas Thursday at youths who hurled stones about 100 yards from the U.S. Embassy there.
Elsewhere, the U.S. Consulate in Berlin was evacuated briefly Thursday after an employee reported a strange smell from a document. German police swept the building but found no dangerous materials.
With tensions still high, most U.S. missions declined to comment on specific security measures, but some changes were visible.
In the Philippines, where hundreds of U.S. troops are advising Filipino forces in their fight against al-Qaida-linked insurgents, U.S. diplomats had asked for additional police and patrols for the embassy compound, as well as a nearby residential complex and the consulate in the central city of Cebu, ahead of the 9/11 anniversary.
U.S. officials said the heightened security would be maintained indefinitely following the attack in Libya.
Guards and Philippine police special forces carrying assault rifles were outside the embassy Thursday, and a pickup truck bearing a machine gun was parked under a tree. Philippine coast guard vessels patrolled nearby Manila Bay. Police patrols were also intensified at other U.S. sites, including the American cemetery in Manila.
In Pakistan, where anti-Americanism is widespread due to drone attacks against militants on Pakistani soil, the senior officer in charge of security in the diplomatic enclave in Islamabad said police would step up surveillance in the area, which includes the U.S. Embassy. "We need to increase manpower and other measures to ensure that no ugly event occurs," Khurram Rasheed said.
At least 10 armored vehicles and 16 police cars could be seen around the massive, fortress-like U.S. Embassy in Amman, Jordan, and a slightly larger number around the Israeli embassy there. Extra armed police also took up positions around the U.S. Embassy in Kuwait, which hosts a substantial U.S. military presence.
Security outside the U.S. Embassy in Algiers was reinforced with several additional police officers. The leader of a dissolved Islamist party was arrested outside the embassy when he tried to deliver a letter there, according to the online news site Tout-sur-l'Algerie.
American officials in Indonesia, the world's most populous Muslim country, warned U.S. citizens to pay close attention to their surroundings and to avoid large crowds, even though there has been no public reaction to the film there so far.
"The movie has hurt Muslims all over the world deeply. They deliberately wanted to make Muslims angry," said Amidan Shaberah, a prominent cleric. "We urge Indonesian Muslims to calm down because the majesty and greatness of God and the Prophet Muhammad will not be diminished by these insults."
An advisory posted on the website of the U.S. Embassy in Kuala Lumpur, Malaysia, another mostly Muslim country, warned that "based on recent events in Cairo and Benghazi, there is the possibility of demonstrations taking place" there, too.
While Americans -- as well as Israelis -- may be top targets for many Muslim extremists, officials from other Western nations also were watching the situation carefully.
German Foreign Minister Guido Westerwelle said security had also been bolstered at his country's embassies and consulates in the Middle East and urged governments there to protect all diplomatic missions. "Diplomats must be able to carry out their work without fear," he said in a televised statement.
In Nigeria, a nation of more than 160 million people largely split between a Muslim north and a Christian south, the U.S. Embassy warned that "extremists may attempt to target U.S citizens and other Westerners."
Previous violence by a radical Islamist sect known as Boko Haram saw the embassy ban travel for its staff to the north for much of this year. The sect is blamed for killing more than 670 people this year alone, according to an Associated Press count.
Nigeria has remained largely quiet in regards to the film, with local media reporting only one small protest in the central city of Jos. Still, Nigeria's federal police force has received orders to provide additional security to foreign embassies.