By Maayan Lubell and Rami Ayyub

JERUSALEM, March 12 (Reuters) - Prime Minister Benjamin Netanyahu on Thursday issued a veiled threat to kill Iran's new supreme leader Mojtaba Khamenei even as he acknowledged that Israel's joint air war with the U.S. may not lead to a collapse of Tehran's clerical government.

Holding his first press conference since the start of the war, the Israeli leader said that Iran was "no longer the same" after nearly two weeks of bombardment and that Tehran had suffered blows to its elite Revolutionary Guards Corps and Basij paramilitary force.

He vowed to keep hitting Lebanon's Hezbollah after the Iran-backed group opened fire on March 2 to avenge Israel's killing of Iran's supreme leader Ali Khamenei - Mojtaba Khamenei's father - at the start of the war.

Standing between two Israeli flags and taking questions over video link, Netanyahu was asked what actions Israel might take against Ayatollah Mojtaba Khamenei and Hezbollah chief Naim Qassem:

"I wouldn't issue life insurance policies on any of the leaders of the terrorist organization ... I don't intend to provide an exact report here about what we are planning or what we are going to do."

As Netanyahu spoke, sirens warning of incoming missile fire from Iran blared across much of central Israel.

Israel has said the aim of its assault on Iran is to eliminate what it views as the existential threat posed by Tehran's nuclear and ballistic missile programmes. It also says it wants to cause a collapse of government by encouraging Iranians to rise up.

While many Iranians want change and some openly celebrated the death of Ali Khamenei, whose security forces killed thousands of anti-government protesters just weeks ago, there has been no sign of protest since the war began.

Asked whether Israel was arming opponents of Iran's rulers and whether it might fail to achieve a collapse of government, Netanyahu said that even if the government did not fall, it would remain weak.

"I will not detail the actions we are taking. We are creating the optimal conditions for toppling the regime but I won't deny that I can't tell you with all certainty that the people of Iran will topple the regime - a regime is toppled from the inside," Netanyahu said.

"But we can definitely help and we are helping."

Posted by: AAngeles/NET25 News