Israeli Foreign Minister Tzipi Livni, a contender to become prime minister, has said Syria must immediately stop arming Hizbullah and backing the Palestinian movement Hamas.

Syria must take "immediate" steps to prove that it is serious about its indirect peace talks with Israel, Livni told CNN Sunday.

She said Damascus must stop supplying Hizbullah with arms and refrain from backing "terrorist" organizations like Hamas.

Livni also urged the international community to act quickly on new sanctions against Iran, which backs Hizbullah.

"The international community is being watched, not only by Iran, but also by Iran's neighbors. And when the international community shows hesitation, this is being perceived as weakness," she told CNN.

Livni expressed concern that if Iran is not challenged over its nuclear drive then Tehran's moderate neighbors are likely to become its allies.

"We live in a neighborhood in which whether you beat the bully or join it," she said.