WASHINGTON AND BEIRUT — Ratcheting up pressure to halt a bloody crackdown on pro-democracy protesters, the Obama administration for the first time slapped economic sanctions on Syrian President Bashar Assad and his top aides.
The penalties announced Wednesday, a day before President Obama is to deliver a major speech on the sweeping political turmoil in the Arab world, suggest that the White House is giving up hope that the measured approach it has taken so far can persuade Assad to allow greater freedoms and break his alliance with Iran.
In a letter to Congress, Obama called the sanctions a response to "continuous escalation of violence against the people of Syria." However, he stopped short of calling for Assad to step down.
The sanctions came as violence broke out late Tuesday and Wednesday in the western city of Homs and the far northern city of Aleppo, where students clashed with plainclothes security forces.
A nationwide strike, to be followed by a day of demonstrations Friday, had mixed results. Merchants and workers in the cities of Homs, Idlib, Qamishli, Dara and Baniyas stayed home, according to Syrian activists. But daily life was unaffected in Damascus, the capital.
"Damascus didn't participate in the strike because as the capital, it is the home of centralized security and intelligence forces and this leaves no room for dissent," said Shaheen, an activist reached in Syria via Skype. He asked that his last name not be published.
The latest U.S. sanctions target Assad, the vice president, prime minister and interior and defense ministers, as well as the directors of military intelligence and the political security forces. The measure freezes any assets they hold in U.S. jurisdiction, and make it illegal for Americans to do business with them.
The Syrian regime is not known to keep significant assets in U.S. banks or investments, so the move is mostly a message that it is facing growing isolation from the international community.
Treasury officials could offer no estimate of how much money Assad and his ministers have in the United States; analysts said their money was more likely to be in Europe or the Middle East. The European Union is expected to tighten its own sanctions as a result of the U.S. action, officials said.
The Obama administration has condemned the violent crackdown by Syrian security forces and several weeks ago it imposed similar sanctions on second-tier officials in Damascus. But it had faced growing criticism on Capitol Hill and elsewhere for not acting more forcefully. Human rights groups say the Assad government has killed more than 800 protesters since demonstrations erupted two months ago after pro-democracy revolutions that ousted autocratic rulers in Tunisia and Egypt.
In his speech Thursday, Obama will seek to explain his varying responses to the wave of uprisings that have spread across North Africa and the Middle East this year, ranging from relative caution with Syria and Bahrain, to strong words with Egypt, to spurring an international military operation in Libya.
The sanctions "send an unequivocal message to President Assad, the Syrian leadership, and regime insiders that they will be held accountable for the ongoing repression and violence in Syria," David S. Cohen, the Treasury Department's top sanctions official, said in a statement.
The administration hinted that it may soon urge Assad to give up power, but other signs suggest U.S. officials still hope that he will reform his regime, one of the harshest dictatorships in the region.
Cohen said Assad and his government "must immediately end the use of violence, answer the calls of the Syrian people for a more representative government, and embark upon the path of meaningful reform."
Middle East experts said the mixed message reflects U.S. anxieties -- and that of many of its Middle East allies -- that Assad's ouster could lead to sectarian warfare in Syria, or perhaps an even more repressive government. They also warn that Assad may cling to power despite international pressure, and may react by fomenting violence in neighboring Israel and Lebanon.
David Schenker, a former Pentagon advisor on the region now at the Washington Institute for Near East Policy, said the administration "still hasn't gone all the way; they continue to have only one toe in the pond here.... It's bizarre."
Steven A. Cook, a Middle East specialist at the Council on Foreign Relations, said the reluctance to call for Assad's ouster was "curious." U.S. officials, he said, "clearly are concerned about the threat of chaos, and want to defer to the neighbors."
The Treasury also broadened the sanctions imposed last month to cover 10 more individuals and groups for alleged roles in human rights abuses and repression in Syria.
The new targets include two senior officials of Iran's Revolutionary Guard, which U.S. officials believe has aided the Syrian regime in its crackdown.