Syrian tanks mounted with machine guns fired on a city at the center of the country's uprising Thursday, defying a day-old agreement between the Syrian government and the Arab League to end nearly eight months of bloodshed, activists said.
At least 12 people were killed in the tank fire and other violence in Homs, according to two main Syrian activist groups.
A crackdown on dissent and what appears to be growing sectarian bloodshed has turned Homs, Syria's third-largest city and home to some 800,000 people, into one of the country's deadliest areas.
The opposition vowed to flood the streets Friday to test whether the regime will stop using force against peaceful protesters.
"May Friday be the day where all streets and squares become platforms for demonstrations, and for the peaceful struggle toward achieving the downfall of the regime," said a Syrian activist coalition called the Local Coordinating Committees.
The uprising shows no signs of stopping despite a government crackdown that the U.N. estimates has killed some 3,000 people. The capture and death of ousted Libyan leader Moammar Gadhafi last month only served to invigorate the Syrian protesters, many of whom carry signs and chant slogans warning President Bashar Assad that he will be the next dictator to go.
At least 12 people were killed when tanks opened fire in Homs on Thursday, according to the British-based Syrian Observatory for Human Rights and the activist coalition called the Local Coordinating Committees.
The latest bloodshed cast a pall over the Arab League accord announced Wednesday in Cairo.
Under the plan, the Syrian government agreed to pull tanks and armored vehicles out of cities, stop violence against protesters and release all political prisoners. Syria also agreed to allow journalists, rights groups and Arab League representatives to monitor the situation in the country.
The proposal is the latest in a string of international efforts to ease the crisis, which has led to wide condemnation of the regime. European Union and U.S. sanctions are chipping away at Syria's ailing economy, and many world leaders have called on Assad to step down.
In Washington, State Department spokeswoman Victoria Nuland harshly criticized the Assad regime, saying it "has a long, deep and continued history of broken promises, and it has significant blood on its hands." She praised the Arab League initiative, "but we have not seen any evidence that the Assad regime intends to live up to the commitments that it's made."
Many critics say Damascus has no intention of abiding by the agreement and is simply buying time.
"We informed the (Arab League's) secretary-general of our concerns about the regime's lack of credibility to carry out the proposal, notably the city of Homs was attacked yesterday and today," said Samir Nashar, who headed the opposition's talks with the Arab League.
A spokesman for the Syrian opposition in Cairo, Momen Kwafatiya, said Syria's approval of the Arab League proposal is a maneuver to avoid having its membership suspended or frozen in the Arab body, something that Gulf countries have quietly been pushing for.
"The (Arab League) decision did not meet the aspirations of the Syrian people," he said.
In accepting the initiative, Assad may be counting on the opposition's shortcomings to give him time to ride out the uprising. Regime opponents in Syria are a diverse, fragmented group, and the opposition is struggling to overcome infighting and inexperience.
Assad, 46, still has a firm grip on power, in part because he retains the support of the business classes and minority groups who feel vulnerable in an overwhelmingly Sunni nation.
Syria blames the bloodshed on "armed gangs" and extremists seeking to destabilize the regime in line with a foreign agenda.
The government has largely sealed off the country from foreign journalists and prevented independent reporting, making it difficult to confirm events on the ground. Key sources of information are amateur videos posted online, witness accounts and details gathered by activist groups.
Violence in Homs earlier this week suggests Syria is sliding toward chaos amid increasing signs that religious and sectarian tensions are growing.
Syria has a volatile sectarian divide, making civil unrest one of the most dire scenarios. The Assad regime is dominated by the Alawite minority, an offshoot of Shiite Islam.
Alawite control has bred resentments, which Assad has worked to tamp down by pushing a strictly secular identity. But he now appears to be relying heavily on his Alawite power base, beginning with highly placed relatives, to crush the resistance.
For many Syrians, the uncertainty over the future is cause for alarm in a country with a fragile jigsaw puzzle of Middle Eastern backgrounds including Sunnis, Shiites, Alawites, Christians, Kurds, Druse, Circassians, Armenians and more.
Although Assad's hold on power appears to be firm for now, he is taking increasingly desperate measures to safeguard his grip. Syria has planted land mines along parts of its border with Lebanon and disrupted Internet and telephone service. Some activists have accused Syrian security forces of arresting wounded protesters and even the doctors who treat them.
Syria's Minister of Health, Wael Nader Halki, denied reports of security forces entering hospitals to make arrests.
"There have been no arrests from the hospitals," he told The Associated Press on the sidelines of a World Health Organization meeting in Geneva on Thursday.
Diplomats attending the meeting stressed the technical nature of the event at a time when Syria is increasingly shunned in other United Nations forums such as the Human Rights Council over its crackdown on protesters.
WHO chief Margaret Chan said she hadn't raised the issue of arrests in hospitals with the Syrian delegation.
"I hear the story from two sides. I stay neutral," she told the AP. But she added that "health care workers should be given the space to provide care to people. I say this to all countries."
Associated Press writers Frank Jordans in Geneva and Matthew Lee in Washington contributed to this report.