U.S. Secretary of State Hillary Clinton said on Sunday that the opposition in Syria was not yet united, vowing to continue to keep up pressure on the Assad regime.

In an interview with CNN, Clinton said that the opposition in Syria, including the Syrian National Council, was not yet the kind of united opposition force that had ousted former Libyan leader Muammar Gaddafi last year.

She said that the Libyan opposition, led by the country's National Transitional Council and based in the city of Benghazi, gave the West "an address" to deliver support to.

"We don't have that in Syria," she said. "The Syrian National Council is doing the best it can but obviously it is not yet a united opposition."

Meanwhile, Clinton vowed that the United States would continue to work with its partners to keep up pressure on the Assad regime.

Participants from 60 countries and regions, including Clinton, gathered at the first Friends of Syria Conference in Tunisia's capital Tunis from Friday, calling for an immediate cease-fire in order to allow humanitarian aid into the country. The group also recognized the Syrian National Council (SNC) as the "legitimate representative" for the Syrian people.

U.S. President Barack Obama vowed on Friday that he would continue to keep up the pressure on the Syrian government and use "every tool available" to stop the killings in Syria.