The US president has extended sanctions against certain Syrian and pro-Syrian individuals, due to what he called their continued interference in neighbouring Lebanon.
Barack Obama decided to keep the sanctions in place for another year despite some encouraging steps by Syria in recent months, the White House said on Friday.
"In the past six months, the United States has used dialogue with the Syrian government to address concerns and identify areas of mutual interest, including support for Lebanese sovereignty," Obama said in a statement.
He said that had been "positive developments in the past year including the establishment of diplomatic relations and an exchange of ambassadors between Lebanon and Syria".
But Obama said that some Syrians and their supporters "continue to contribute to political and economic instability in Lebanon and the region and constitute a continuing unusual and extraordinary threat to the national security and foreign policy of the United States".
Engaging Damascus
Obama extending sanctions that were imposed on August 1, 2007 by George Bush, his predecessor.
The restrictions place a freeze on the assets of individuals accused of harming Lebanon's sovereignty on Syria's behalf.
The move to keep the sanctions in place comes as the Obama administration aims to improve relations with Syria, an ally of Iran.
George Mitchell, the US special envoy to the Middle East, met Bashar al-Assad, the Syrian president, earlier in the week in an attempt to encourage Damascus to become further involved in the regional peace process.
The Obama administration recently relaxed trade sanctions against Syria as part of a move to engage with Damascus.
Syrian army troops and intelligence officers were pulled out of Lebanon in 2005 after a 29-year presence in the country, in the wake of public anger at the assassination of Rafiq al-Hariri, a former Lebanese prime minister.
Damascus has denied having any involvement in Hariri's death, which is the subject of a UN-mandated special tribunal in the Netherlands.