JOIN USAsset freezes and bans on business interactions were imposed on Foreign Minister Walid Muallem, top presidential advisor Bouthaina Shaaban, and Syrian ambassador to Lebanon Ali Abdul Karim Ali, the Treasury said.
"Building on our sanctions targeting the entire government of Syria, we are bringing additional pressure to bear today directly on three senior Assad regime officials who are principal defenders of the regime's activities," said Treasury Under Secretary David Cohen.
The new sanctions follow an August 18 order signed by President Barack Obama that froze all Syrian state assets inside the United States and forbade investment and exports to the country, due to the Assad government's deadly crackdown on anti-government protesters.
It also banned imports of oil and gas from Syria, aiming to hurt a key revenue stream for the Assad regime.
The attacks on protesters "constitute an unusual and extraordinary threat to the national security, foreign policy and economy of the United States," the presidential order said.
Today's sanctions announcement was one of a series of such actions over the past several months designed to raise pressure on the Syrian government to bow to pressures for democratic reforms or even step aside for a new leadership.
The sanctions have been matched by similar blacklisting from Europe, which yesterday moved to ban oil imports from Syria.
Earlier today, too, EU foreign policy chief Catherine Ashton urged Assad to stop the violent crackdown on protesters.
But Damascus appears determined to ignore the pressure.Since yesterday more than two dozen people have been killed and dozens more wounded by security forces in crackdowns on end-of-Ramadan protests, according to various rights groups.