By Parisa Hafezi and John Irish DUBAI/PARIS (Reuters) -While rising U.S.-Iran tensions over Tehran's uranium enrichment jeopardize nuclear talks, three Iranian sources said on Tuesday that the clerical leadership lacks a clear fallback plan if efforts to resolve a decades-long dispute collapse.

Iran's Supreme Leader Ayatollah Ali Khamenei slamm ed U.S. demands that Tehran end its uranium enrichment program, stating that he does not believe ongoing nuclear negotiations with the U.S. will yield results. Iran says its nuclear program is for civilian purposes and that its enrichment program is a source of national pride and not negotiable.

New U.S. intelligence has raised alarm bells, suggesting Israel may be preparing a strike on Iranian nuclear facilities. The revelations, reported by CNN, cited multiple U.S. officials tracking movements of air munitions and Israeli military drills.

The U.S. and Iran remain locked in a standoff over uranium enrichment ahead of a potential new round nuclear talks.

A US media outlet reports that Israel may be poised to strike Iran’s nuclear sites and oil markets wince. In Washington, a Republican administration wonders if Tehran is more determined or deterred.

World shares were mixed Wednesday while oil prices jumped more than 1% after a report by CNN said Israel may be planning an attack on Iranian nuclear facilities. A CNN report cited unnamed intelligence officials saying Israel may be preparing for an attack on Iranian nuclear facilities.

Iran's ratification of a 20-year pact with Russia marks a major step in expanding military and economic ties amid tensions with the West