The US has imposed economic sanctions on a top Syrian businessman days after President George W Bush authorised new penalties against the country.
Damascus has been under Bush administration sanctions since 2004
Washington is seeking to punish key figures in Syria for their alleged efforts to undermine the governments of neighbouring Iraq and Lebanon.
The sanctions affect Rami Makhlouf, a first cousin of President Bashar Assad and one of Syria's most powerful men.
No immediate response from officials in Damascus was reported.
The US Treasury Department order freezes any assets that Mr Makhlouf holds in US financial institutions and prohibits US citizens and firms from engaging in any business contacts with him.
Mr Bush signed his executive order on 13 February, a day after veteran Hezbollah militant Imad Mughniyeh was killed in an unclaimed car bombing in Syria nearly 15 years after dropping out of sight.
Mughniyeh had been suspected of attacks that killed hundreds of Americans in Lebanon as well as the kidnappings of Westerners.