CAIRO – Defying tanks, troops and gunfire, thousands of people took to the streets Friday across Syria to protest the regime’s bloody crackdown on a 6-week-old uprising and press a demand for the ouster of President Bashar Assad, according to witnesses, activists and news reports.

More than 60 people were killed, according to human rights activists; about half of them were gunned down as they tried to breach a blockade by tank-backed soldiers in Daraa, the southern city where the gravest challenge to more than four decades of Assad family dictatorship began.

“There’s a difference between Daraa and everywhere else,” said Haitham al Maleh, an 80-year-old dissident, reached by telephone in Damascus, which has banned most foreign journalists.

In the first concrete international response to the crackdown, the Obama administration announced sanctions against three top Syrian security officials, including Assad’s brother, as well as the Quds Force of Iran’s Islamic Revolutionary Guard Corps, accused by the White House of advising the regime on crowd suppression.

The sanctions freeze any U.S. assets belonging to the targets, and prohibit Americans from doing business with them. Because they aren’t believed to have any U.S. assets, the measures are mostly symbolic, although they carry political weight that would bolster sanctions that are being considered by the European allies.

The Obama administration has been criticized for failing to respond to the uprising in Syria — where more than 450 people have reportedly been killed and four times that number injured — with the same alacrity as it did to the revolutions in Tunisia, Egypt and Libya.

“Our goal is to end the violence and create an opening for the Syrian people’s legitimate aspirations,” White House spokesman Tommy Vietor said of the sanctions. “These are among the U.S. government’s strongest available tools to promote these outcomes, and we are seeking support for similar actions by other governments.”

Assad was not included in the sanctions. But a senior Obama administration official said that the measures could be extended to the 46-year-old leader.

“Don’t think for a second Bashar is not on our radar, and that if these abuses continue we won’t sanction him,” said the senior official, who requested anonymity because he was not authorized to discuss the issue publicly.

In another action, the administration revoked a number of export licenses approved for Syria, including one that would have allowed the regime to purchase a luxury aircraft believed intended for Assad’s personal use.

In Geneva, the United States also won approval of a resolution by the U.N. Human Rights Council condemning the crackdown and authorizing the body to investigate the Assad regime’s alleged human rights abuses.

While some security forces have been killed, “the preponderance of information emerging from Syria depicts a widespread, persistent and gross disregard for basic human rights by the Syrian military and security forces,” Deputy U.N. Human Rights Commissioner Kyung-wha Kang told the 47-nation body.

The protests began Friday after worshippers left mosques following prayers in the capital, Damascus, and other cities around the country of 21 million, according to news reports and activists, who said that troops, police and pro-regime gunmen responded with gunfire and clubs.

Maleh, who has remained in his Damascus home since being freed from prison more than a month ago, said the day showed international and national opposition to the regime.

“There are protests all over the place, and it’s important because in the biggest cities there were protests,” he said, referring to marches in Damascus and Aleppo. Demonstrations also were reported in Homs and the coastal cities of Baniyas and Lattakia.