The United States is exploring tough new sanctions against Syria in a bid to force it to cease its "brutality" against protesters, U.S. Secretary of State Hillary Clinton said.
Clinton's comments came as Syrian security forces continued their siege of the central city of Hama. Residents and rights campaigners say about 137 people have been killed throughout Syria in the past three days, most of them in Hama. More than 1,600 civilians are thought to have been killed since protests against the regime of President Bashar al-Assad began in March.
Clinton met with the U.S.-based representatives of Syria's fledgling opposition in Washington on Tuesday, who said the White House should do more to help stop the killing.
The U.S. is weighing new sanctions that would "isolate the Assad regime politically and deny it revenue with which to sustain its brutality," Clinton said in a statement after the meeting.
"We need President [Barack] Obama to address the courage of the Syrian people in the street and ask Bashar al-Assad to step down immediately," said Radwan Ziadeh, one of the activists who met with Clinton.
Washington has already imposed sanctions on Assad and members of his government. A group of U.S. senators introduced a bill on Tuesday that would expand sanctions on Syria's energy sector.
The European Union tightened its sanctions against Syria on Monday but the UN Security Council failed to reach a resolution condemning the Syrian regime.