Iran''s top leader banned hardline Iranian volunteers on Thursday from leaving the country to carry out suicide bombings against Israel, but warned that Iran would assist the militant group Hamas in other ways.

Ayatollah Ali Khamenei''s ban sought to tone down calls by allies of hardline President Mahmoud Ahmadinejad to toughen Iran''s stand against Israel.

But it also exposed hidden rifts between the supreme leader and the president five months before elections in which Ahmadinejad, whose popularity has been waning, is seeking a second term.

Hardline Iranian student groups had asked the government to authorize volunteers to go carry out suicide bombings in Israel in support of Hamas. The students began signing up after Khamenei issued a religious decree on Dec. 28 saying anyone killed while defending Palestinians in Gaza against Israeli attacks would be considered a martyr.

A week later, Khamenei''s comments sharply contrasted his religious order.

"I thank the pious and devoted youth who have asked to go to Gaza ... but it must be noted that our hands are tied in this arena," Khamenei said on state television. He did not elaborate how Iran would help Hamas in other ways.

The student groups claim that more than 70,000 people throughout Iran have registered as volunteer suicide bombers since Israel launched its assault against Hamas-ruled Gaza on Dec. 27. Israel''s bombardment of Gaza, which has killed more than 700 Palestinians, has outraged many in Iran and the rest of the world.