Moved by escalating violence in Syria, European leaders warned Tuesday that they will impose new sanctions on Damascus unless President Bashar al-Assad halts his bloody crackdown on anti-government protesters.

The warnings reflected a growing sense of outrage in European capitals since Assad sent tanks and armored personnel carriers into the rebellious southern city of Daraa on Monday, firing at youths in the street and inflicting a death toll estimated by human rights activists at two dozen.

The killings brought to more than 400 the number of demonstrators killed since the country erupted in anti-government agitation in mid-March. In addition, the use of army tanks was taken as a signal of Assad’s willingness to resort to even more bloodshed in seeking to restore order.

“The situation has become unacceptable,” French President Nicolas Sarkozy said during a joint news conference in Rome with the Italian prime minister, Silvio Berlusconi. “You don’t send tanks, the army, against demonstrators. You don’t fire on them.”

Berlusconi joined the condemnation, according to news agencies, saying: “Together we send a strong call to Damascus authorities to stop the violent repression of what are peaceful demonstrations, and we ask all sides to act with moderation.”

Officials at the French Foreign Ministry told reporters that Sarkozy’s tone had hardened because of revulsion over the military intervention in Daraa, which was seen as a dangerous escalation. France is seeking “strong measures” to reduce the violence, the officials said, suggesting that Sarkozy’s government was ready to seek European Union sanctions.

The British foreign secretary, William Hague, said in London that Britain also is ready to pursue sanctions against Assad’s government if the violence is not reduced quickly through dialogue with the protesters.

“It can choose ever more violent repression, which can only ever bring short-term security for the authorities there,” Hague told Parliament, according to Reuters news agency. “If it does so, we will work with our European partners and others to take measures including sanctions that will have an impact on the regime.”

Sarkozy’s strong language seemed to signal an end to his attempt to make Assad a more compliant partner in Middle East peace negotiations through displays of friendliness. Soon after his election in 2007, while Assad’s government was largely isolated, Sarkozy invited him to Paris and treated him as a full-fledged interlocutor. The policy, widely condemned at the time, produced no concrete results.

The change in tone also reflected questions raised in France about Sarkozy’s strong position backing military action against Moammar Gaddafi in Libya and why there was no similar urgency for action against Assad.

“We are very tough vis-a-vis Gaddafi and we say nothing vis-a-vis Syria,” said Jean-Christophe Cambadelis, a member of parliament from the opposition Socialist Party. “It is incomprehensible.”

Former prime minister Laurent Fabus, another Socialist Party figure, called for immediate United Nations intervention in Syria, without detailing what he had in mind.

The influencial Paris newspaper Le Monde also pointed out the apparent incongruity in the policies of France and other Western countries. “We tolerate in Damascus what we condemned in Tripoli,” the paper said in a front-page editorial. “This indulgence is no longer possible. As Daraa is martyred, we must isolate and sanction the regime of Bashar al-Assad.”

Responding to the criticism, Sarkozy denied that there were inconsistencies in his policies. He pointed out that the two situations were not identical, but he then did not rule out taking action in Syria, according to news service accounts from Rome.

“That does not mean that we are going to intervene everywhere in the world,” he said. “There is no question of anything as long as there is no Security Council resolution.”