Condemns the government of Syria for hindering and failing to cooperate with the United Nations International Independent Investigation Commission's (UNIIIC) investigation of former Prime Minister of Lebanon Rafik Hariri's assassination. Supports extending UNIIIC's investigative mandate for at least six months. States that insecurity in Lebanon could have a destabilizing effect on the region and harm Lebanon's strengthening of democracy and economic prosperity. Expresses gratitude to: (1) chief investigator Detlev Mehlis and UNIIIC for their continuing efforts to uncover evidence about Rafik Hariri's assassination; and (2) those who have freely assisted the UNIIIC investigation. Demands that Syria commit itself to fulfill all obligations with UNIIIC and with U.N. Security Council Resolutions 1559, 1595, and 1636. Encourages the U.S. Permanent Representative to the United Nations to use U.S. influence in the U.N. Security Council to advocate for the application of punitive measures and sanctions against Syria that target its leadership if Syria fails to cooperate fully with the UNIIIC investigation and continues to violate Resolutions 1559, 1595, and 1636. Urges the U.S. government to support UNIIIC's extension of jurisdiction to include assassinations and assassination attempts in Lebanon since October 1, 2004. Urges the President to implement further measures against the Syrian leadership in accordance with the Syria Accountability and Lebanese Sovereignty Restoration Act of 2003 (Public Law 108-175), particularly if Syria fails to cooperate fully with the ongoing UNIIIC investigation and continues to violate Resolutions 1559, 1595, and 1636.