Syrian leaders deployed tanks and troops against unarmed demonstrators Monday in a sharp escalation of their effort to crush the widening protest movement, prompting the Obama administration to condemn the deadly crackdown and weigh additional sanctions against the embattled government.

The Syrian army entered the city of Daraa, the cradle of anti-government unrest near the border with Jordan, and other southern towns as protesters massed in the streets. According to witnesses and news reports, about 25 demonstrators were killed in Daraa and the coastal city of Jableh, where witnesses said snipers opened fire on the crowd.

Gunfire continued in Daraa on Tuesday as residents took refuge from tanks in the streets and snipers on rooftops, and the government cut off water supplies, news services reported.

Human rights groups said security forces have rounded up hundreds of pro-democracy activists across Syria since Friday’s protests.

In response to the increased violence, the State Department on Tuesday urged Americans in Syria “to depart immediately while commercial transportation is readily available” and advised those who must remain to limit travel within the country. Other Americans “should defer all travel to Syria at this time,” it said in a travel warning. The department also said it has ordered all eligible family members of U.S. government employees and “certain non-emergency personnel” to leave Syria.

The Syrian government’s show of force, the largest in weeks of street demonstrations, is sharpening the choice facing President Obama, who has attempted to balance calls for democratic reform in the Arab world with concerns of allies that have counted on President Bashar al-Assad to preserve stability in the volatile Middle East.

As the death toll mounts, Obama is under pressure to harden his largely reactive policy on Assad and echo demonstrators’ demands that the Syrian leader must go. Human rights groups say more than 300 people have been killed in the Syrian crackdown so far.

“The brutal violence used by the government of Syria against its people is completely deplorable and we condemn it in the strongest possible terms,” Tommy Vietor, the National Security Council spokesman, said in a statement Monday.

Vietor said that “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 administration has been ratcheting up its criticism of Assad’s response to the popular unrest, now more than five weeks old. But Obama has yet to declare that Assad, who inherited power from his father almost 11 years ago, has lost the legitimacy to rule, as the president declared in the case of Libyan leader Moammar Gaddafi and Egyptian President Hosni Mubarak, a U.S. ally.

“We very much see our role in these things as one that is behind what the voices in the region are saying,” said one administration official, who like others spoke on the condition of anonymity to describe internal thinking.

Administration officials say a majority of those taking part in Syria’s demonstrations have begun calling for Assad’s departure, an escalation of the movement’s initial demand for more civil rights and political freedoms under the existing government.

The tipping point may have come in the weekend of violence, giving Obama the popular cover he has sought before calling for regime change in the Arab world.

“We’re not there yet,” the administration official said. “This will be event-driven.”

Obama’s reluctance is rooted in fear of what might replace Assad, a member of Syria’s minority Alawite sect who is running a Sunni-majority country with a prevalent, if repressed, Islamist strain in its society and politics.

His secular Baath Party has been viewed by neighbors as a bulwark against Islamic extremism, making his government a linchpin in the region. Many U.S. allies, including Israel, Saudi Arabia and Turkey, hope that Assad finds a way to remain in power.

Administration officials, meanwhile, have argued that they have few tools available to influence Assad’s government.

The George W. Bush administration imposed stiff financial sanctions against Syria in 2004, squeezing its banking sector.

Although its leverage is limited, the Obama administration is considering additional sanctions, including a ban on spare parts for Syria’s commercial and private aircraft fleet, according to people who have been briefed on options.

Most analysts, however, say the administration must press the European Union, Syria’s leading trading partner, to impose sanctions against Assad’s government, particularly against its small but financially vital oil sector.

“Anything is more effective when it’s made multilateral,” said a second administration official, who is involved in Middle East policy. “This is something that we will definitely be looking into.”

In London, British Foreign Secretary William Hague said Tuesday that his country is working with its international partners on the U.N. Security Council, in the European Union and the Middle East on “possible further measures” to persuade Syrian authorities “to stop the violence and respect basic and universal human rights.”

The U.N. Human Rights Commission is scheduled to hold a session Tuesday on Syria, and the United States will push the body, known for its criticism of Israel, to condemn Assad’s crackdown.

Some analysts question whether Assad, an ophthalmologist by training who nurtures a cosmopolitan, reformist image, is still running the security services or whether his brother, Maher, is directing the crackdown through the special forces he controls.

Administration officials say Assad is firmly in charge.

“He’s calling the shots, there should be no confusion about that,” the second official said. “They are all working together, but he calls the shots.”

But, the official added, “we’re keeping a careful eye on signs of the government splintering.” Two Syrian legislators have resigned in protest of the government’s policy, a public break the administration official called “significant.”

There were reports Monday of divisions within the armed forces in Daraa as some soldiers apparently refused to carry out what appear to be “shoot to kill’” orders.

A White House official aware of the situation said the refusal is “not really a reflection of divided orders, but of personal feelings of some of the soldiers who do not want to open fire on their own people.”

The escalating crackdown follows Assad’s decision last week to lift the decades-old emergency laws, tools the government has used to stifle dissent.

Assad has fired the governors of Daraa and Homs and sent security forces into a growing number of towns and cities. As tanks rolled in Daraa and Arwa on Monday, the minister of information in neighboring Jordan said the border had been closed, though Syrian officials denied the assertion.

Human rights advocates said all communications into the costal city of Jableh and within the town have been cut, leaving it isolated and unprotected from the armed gangs associated with the Assad family that witnesses said are patrolling the streets.

“I think this operation launched by the army and security will go on for a few days,” said Wissam Tarif, the executive director of Insan, a human rights organization with a team of activists working throughout Syria. “Now they moved to Plan B — eliminate the movement and build the wall of fear again.”

Douma, a suburb of Damascus, remains under siege by security forces, which have raided private homes in the past two days.

“This is a return to Hama,” said one woman, who asked not to be named for security reasons. In 1982, then-President Hafez al-Assad — Bashar’s father — ordered the killings of as many as 25,000 people in the central city of Hama during a Muslim Brotherhood uprising against the government.

State TV carried images of Assad meeting leaders of religious sects over the weekend in an attempt to portray a sense of unity among the country’s minorities.

But the reality on the ground is far different.

In Moadamiya, a town six miles southwest of downtown Damascus, at least seven tanks and several more armored personnel carriers have been stationed on the outskirts.

Soldiers have set up campsites and are checking passing vehicles. Locals are being strip-searched as they enter the town. Soldiers have been drawn from other regions to decrease the possibility of sympathy growing in the ranks.

“There is no going back to the way things were now,” said a woman in Damascus who works in a pharmacy. “We no longer believe what we are being shown on state television. We are not stupid. We know bad things are happening in the country.”

A special correspondent in Damascus, Syria, contributed to this report.