Mr. Obama’s executive order — along with additional sanctions imposed by the Treasury Department against Syrian and Iranian intelligence services and commanders — reflected the growing American frustration that Mr. Assad’s government was not heeding international condemnation and seeking a peaceful resolution to the popular uprising in the country.
Until now, Mr. Obama had adopted a much more measured and cautious approach than he did in Libya in hopes, officials said, that Mr. Assad would respond to international pressure. The administration clearly concluded that approach was not working.
Though the move may prove largely symbolic, it represents a significant step in isolating a government that has long sought to entrench itself during its worst crises, then rehabilitate itself when danger passes.
The sanctions may make that more difficult.
“The actions the administration has taken today send an unequivocal message to President Assad, the Syrian leadership, and regime insiders that they will be held accountable for the ongoing violence and repression in Syria,” David S. Cohen, acting under secretary for terrorism and financial intelligence, said in a statement.
The sanctions freeze any assets that Mr. Assad and the others have in American financial institutions, and prohibit trade with them. Similar sanctions against Libya’s leader, Col. Muammar el-Qaddafi, led to the seizure of more than $30 billion in assets, though it is believed that Mr. Assad has far fewer vulnerable assets. In addition to him, the sanctions affect the vice president, the prime minister, the interior and defense ministers, and the directors of military intelligence and political security.
The sanctions come amid growing signs that the government feels emboldened after staggering in the face of an unprecedented challenge to 40 years of rule by the Assad family. Officials have said they believe they have the upper hand and talk in weeks, not months, about putting an end to protests that erupted across the breadth of the country, from the southern steppe and Mediterranean coast to the outskirts of Damascus.
In an interview published Wednesday with a privately owned Syrian newspaper, aligned with the government, Mr. Assad declared that the tumult was coming to a close and acknowledged that his security forces had made mistakes in a crackdown so broad that hundreds of detainees were being held in schools and soccer fields.
Human rights activists have said at least 700 people were killed and 10,000 people arrested, as the military laid siege to at least four towns and cities.
“President Assad gave assurances that Syria had overcome the crisis it went through and that events were coming to an end,” the daily quoted him as saying.
The president also told the delegation that 4,000 police officers were undergoing what it called training to “prevent these excesses,” without giving further details.
Steven Lee Myers reported from Washington and Anthony Shadid from Beirut, Lebanon. Hwaida Saad and a New York Times employee in Beirut contributed reporting.
