Israel's foreign minister says Israel will act immediately if it discovers Lebanese Hezbollah militants are raiding Syria's chemical or biological weapons stocks.

Avigdor Lieberman told Israel Radio on Wednesday: "For us, that's a casus belli, a red line."

Israel's political leaders have been warning in recent days that they would be prepared to strike weapons depots to keep those arms from reaching militants. They fear Hezbollah and other militants could raid those arsenals if the central government in Syria collapses amid intensifying violence.

Israel's military chief, however, counseled restraint on Tuesday, warning that an attack on Syrian chemical weapons depots could drag Israel into a broader war. Israel currently assesses that Syria retains control over these arsenals.