Washington has tried to isolate Bashar Assad's government

President George W Bush accused Syria's government of undermining international efforts to stabilise Iraq and of continuing its occupation of Lebanon.

He said Syria continued to represent an "extraordinary threat" to the US.

A broad range of sanctions against Damascus were brought in by President George W Bush a year ago.

They include a flight ban to and from the US, the authorisation to freeze the assets of Syrian nationals and restrictions on banking relations between the two countries.

Humanitarian items such as food and medicine are not affected by the sanctions.

In a letter to the congressional leaders, Mr Bush said Syria poses a "continuing, unusual and extraordinary threat to the national security, foreign policy and economy of the US".

He accused the Syrian government of "supporting terrorism, pursuing weapons of mass destruction and missile programmes, undermining United States and international efforts with respect to the stabilisation and reconstruction of Iraq, and with respect to Lebanon".