Bush on Thursday extended a ban on certain US exports to Syria and other sanctions that were imposed on 11 May 2004, to "beyond 11 May 2005" but did not specify a date.
The sanctions severed banking relations with the Commercial Bank of Syria, froze assets of Syrians suspected of involvement in terrorism or the development of weapons of mass destruction, and prohibited Syrian flights to and from the United States.
Bush accused Syria of supporting terrorism, pursuing weapons of mass destruction, undermining efforts to stabilise Iraq and "continuing its occupation of Lebanon" and said this posed a "continuing, unusual and extraordinary threat" to the United States.
The US demanded Syria remove all its troops and intelligence officers from Lebanon after the 14 February assassination of former Lebanese Prime Minister Rafiq al-Hariri.
Syria ended its 29-year military presence in Lebanon last week.