The United States has hardened its tone on Syria's political crackdown, raising the prospect of targeted sanctions, but still declined to call for President Bashar al-Assad to go.
Washington also defended the presence of an American ambassador in Damascus, who only arrived after a six-year absence in January, as Assad's security forces deployed tanks and snipers, killing at least 25 people in a key town.
"The brutal violence used by the government of Syria against its people is completely deplorable and we condemn it in the strongest possible terms," said National Security Council spokesman Tommy Vietor.
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"The United States is pursuing a range of possible policy options, including targeted sanctions, to respond to the crackdown and make clear that this behavior is unacceptable.
"The Syrian people's call for freedom of expression, association, peaceful assembly, and the ability to freely choose their leaders must be heard."
Calls to end violence
Washington has issued repeated statements by senior officials including President Barack Obama calling for an end to violence and political reform in Syria, but has faced criticism for not taking more concrete steps.
But Monday's crackdown appeared to mark a point at which the administration -- which has sought to engage Syria as a key regional power player -- had little choice but to be seen to act more robustly.
As well as the crackdown in the town of Daraa, a focal point of protests, Syrian troops also on Monday launched assaults on the Damascus suburbs of Douma and Al-Maadamiyeh, witnesses said.
New US sanctions would have a strong symbolic element but the Wall Street Journal reported that they would not have much impact on Assad's inner circle as few regime kingpins have substantial holdings in the United States.
But should similar measures be adopted by Europe, they could have more bite, given more substantial holdings in the continent by the Assad family, the paper said, adding the US move could pressure European governments for action.
Sanctions in place
Syria is already subject to American sanctions, aid restrictions and export bans, due to its presence on Washington's list of state sponsors of terrorism.
So far, Washington has not threatened to recall its ambassador to Syria, a post filled in January after a six-year absence, as Obama sought to court Damascus as part of a broader Middle East diplomatic push.
White House spokesman Jay Carney said that the presence of the ambassador had allowed Washington to make its stance clear to the Assad government.
"Having an ambassador in Syria has allowed us to be in Syria, basically, in the presence of the government to make our views known directly and not be a long distance (away)."
No call to leave
Carney was also pressed on why Obama had not personally called for Assad to heed calls of protestors and leave -- raising an apparent contradiction with US policy in Libya, which has seen the president call for Muammar Gaddafi's ouster.
"Libya was, again, a unique situation," Carney said.
"We had large portions of the country that were out of the control of Muammar Gaddafi, we had a Gaddafi regime that was moving against its own people in a coordinated military fashion and was about to assault a very large city."
Carney also argued that there had been an international consensus to act in Libya.
The crackdown in Syria poses a dilemma for the Obama administration, which has found its regional policy repeatedly challenged by unrest in the Middle East.
On the one hand, Washington could stand to profit from a fall of Assad's minority Alawite regime, which is allied to Shiite Iran, a longtime US foe, and which wields power detrimental to US goals in Lebanon.
On Friday, Obama accused Syria of blaming outsiders for its troubles, and specifically said it was seeking Iranian help to suppress its citizens.
But though it may welcome a weakening of Syrian ties to Iran, Washington also appears concerned about the uncertainty of what could follow a fall of the Assad regime amid fears of an even more radical government.
The United States had appeared to hope that eventual Syrian talks with Israel could help pave the way for a future Middle East peace compact and that Assad could be coaxed towards reform and dialogue.
Some 390 people have been killed in security crackdowns since protests erupted in Syria in mid-March, according to rights activists and witnesses.
