The clock is ticking for senior clerics seeking a successor to Iran's Supreme Leader Ayatollah Ali Khamenei.

A three-man committee from a top clerical body, appointed by Khamenei himself two years ago to identify his replacement, has accelerated its planning in recent days since Israel attacked Iran and threatened to assassinate the veteran leader, five insiders with knowledge of the discussions have said.

Khamenei, 86, is being regularly briefed on the talks, according to the Iranian sources who requested anonymity to discuss highly sensitive matters. He has gone into hiding with his family and is being guarded by the Vali-ye Amr special forces unit of the Revolutionary Guards, a top security official said.