IRAN'S supreme leader has pledged to confront and defeat the ''cancerous tumour'' of Israel as international concern grows of a pre-emptive Israeli strike on the Islamic regime's nuclear installations as early as April.

In a speech, Ayatollah Ali Khamenei on Friday defied international sanctions aimed at his country's suspected atomic weapons agenda and promised to retaliate if Israel or the US opted for military action.

Ayatollah Khamenei Credit:AFP

His threats came as US Defence Secretary Leon Panetta reportedly spoke of a ''strong likelihood'' of Israel unilaterally striking at Iran's nuclear facilities in ''April, May or June''.

Amid signs of a growing rift between Israel and Washington over the use of military force to contain Iran's nuclear ambitions, Mr Panetta said: ''Israel has indicated they're considering this and we have indicated our concerns.''