(Reuters) - The United States and Israel have postponed a joint military exercise due to be held in the coming weeks until later in the year, an Israeli security source told Reuters Sunday.

I can confirm the exercise has been postponed, probably to the end of 2012, said the source, who declined to be named.

The air-defense drill, named Austere Challenge 12, is expected to be the largest-ever exercise between the two allies, who regularly hold joint military maneuvers.

Israeli media reports originally said it was cancelled due to budgetary constraints, but some pundits speculated that the real reason was to avoid further raising tensions with Iran, although when asked, the source ruled this out.

It's for a host of reasons, mainly logistical, but not the reason you cited (tensions with Iran). Israel and the U.S. are expected to be putting out a joint statement soon, the source said.

Israel sees the makings of a mortal threat in Iran's uranium enrichment and missile projects, and the Jewish state's leaders have not ruled out the use of military force to stop it.

Iran says its nuclear program is solely for peaceful purposes.

Tensions between Washington and Tehran have risen in recent weeks after U.S. President Barack Obama signed a bill on New Year's Eve that, if fully implemented, would make it impossible for most countries to pay for Iranian oil.

Iran has threatened to close the Strait of Hormuz, the world's most important oil shipping lane, if sanctions prevent it from exporting oil. The United States has said it will not tolerate such a move.

(Reporting by Dan Williams; Writing by Ori Lewis; Editing by Peter Graff)