The U.S. State Department urged American citizens to leave Syria immediately on Thursday, citing ongoing uncertainty and volatility in the country.
Americans who could not leave Syria were urged to limit nonessential travel.
All eligible family members of U.S. government employees and some non-emergency personnel were ordered out of the country last April.
Opposition council formed
Earlier Thursday, a group of Syrian opposition activists announced the creation of a council designed to present a united front against President Bashar Assad's regime, which has waged a bloody crackdown on anti-government protesters during the past six months.
The Syrian opposition consists of a variety of groups with often differing ideologies, including Islamists and secularists, and there have been many meetings of dissidents who say they represent the opposition. But activists said the new "Syrian National Council," formed during a meeting in Turkey, is the most serious initiative aimed at bringing revolutionary forces together.
The United States gave its support, noting the difficulties the groups are facing.
"Any opposition movement in Syria faces tremendous obstacles," State Department spokesman Mark Toner said. "It's very hard for them to organize politically and to draft and communicate a platform while their members and leaders are being hunted down and killed."
The council groups some 140 opposition figures, including exiled opponents and 70 dissidents inside Syria, said Bassma Kodmani, a Paris-based academic. Kodmani added that the council "categorically opposes" any foreign intervention or military operations to bring down Assad's regime.
"We are in agreement over the peaceful nature of the revolution," she said.
A popular uprising began in Syria in mid-March, amid a wave of anti-government protests in the Arab world that have already toppled autocrats in Tunisia, Egypt and Libya. Assad has reacted with deadly force that the U.N. estimates has left some 2,600 people dead.
The meeting in Istanbul took place as Syrian troops carried out raids in the suburbs of the capital Damascus, the central province of Homs and the northwestern region of Idlib that borders Turkey, activists said.
The London-based Syrian Observatory for Human Rights said one person was killed and five were wounded when security forces opened fire during raids in the Damascus suburb of Zabadani. The group said a paramedic who was wounded last week also died in hospital on Thursday.
The new opposition council aims to "convey the Syrian people's just problems on the international platform, to form a pluralist and democratic state," a statement said. It also hopes to bring down the "leadership that is ruling through dictatorship, and to unite the prominent politicians under one umbrella."
The reason it took so long to form the council is that "we wanted to make sure everyone was on board," said Adib Shishakli, an opposition member based in Saudi Arabia. Shishakli said the council would elect a leader at a later time.
Ahmad Ramadan, another opposition member, said the council would form 10 bureaus, including a foreign relations office dedicated to "relaying the demands of the revolution, the people's requests to the outside world." He said it would also work to form a television station to help overthrow the regime.
Louay Safi, a U.S.-based academic, said the council is broad-based and includes Sunnis, Shiites, Alawites, Kurds and members of the Muslim Brotherhood. It is "open to everyone unless they are against democracy," he said.
The emphasis on unity comes amid fears of civil war between Assad's ruling minority Alawite sect and the country's Sunni Muslim majority.
Also Thursday, Syrian state TV aired excerpts of a video showing army Lt. Col. Hussein Harmoush, one of the first officers to defect after the uprising began. The pro-government daily Al-Watan said he was detained during "a special operation" in Idlib.
Harmoush, of the so-called Free Officers Movement, has previously appeared in videos calling on the army to stand by the people instead of the regime.
Meanwhile, French President Nicolas Sarkozy said he dreamed that one day young Syrians will have the same opportunity as young Libyans have for democracy. He made his remarks from Tripoli during his first official visit to Libya since rebels ousted dictator Moammar Gadhafi.
"The best I can do is dedicate my visit here in hopes that everyone in Syria also benefits," he said.
In France, Foreign Ministry spokesman Bernard Valero said Syrian opposition members are meeting in Paris with French officials on Thursday and Friday, though he did not identify the figures or elaborate on the meetings.
Syrian opposition members in Istanbul said they were in contact with France but had no scheduled talks with French officials this week.