Israeli airstrikes killed two successors to Hezbollah's slain leader, Prime Minister Benjamin Netanyahu said on Tuesday, as Israel expanded its ground offensive against the Iran-backed group with a fourth army division deployed into south Lebanon.

Netanyahu spoke in a video his office released hours after the deputy leader of Hezbollah, which is reeling after a spate of killings of senior commanders in Israeli airstrikes, left the door open to a negotiated cease-fire.

"We've degraded Hezbollah's capabilities. We took out thousands of terrorists, including (Hassan) Nasrallah, himself, and Nasrallah's replacement, and the replacement of the replacement," Netanyahu said, without naming the latter two.