The United States should deploy more warships to the Gulf, arm Israel and issue tough warnings to convince Iran it is serious about possible military action to stop Tehran's nuclear program, former US lawmakers and experts said Wednesday.

The bipartisan group criticized President Barack Obama's administration for downplaying the likelihood of US military action in public statements, saying it undercut efforts to pile pressure on Iran's leadership.

Diplomacy and sanctions designed to persuade Iran to abandon its nuclear ambitions would only have a chance to succeed if backed up by more "visible, credible preparations for a military option," the bipartisan group said in a report.

"The United States needs to make clear that Iran faces a choice: it can either abandon its nuclear program through a negotiated arrangement or have its program destroyed militarily, by the United States or Israel," said the report by a panel led by former senator Chuck Robb, a Democrat, and Charles Wald, a retired US general.

"The risks of inaction are too high. We must stop Irans nuclear clock," it said.

The authors found fault with the Obama administration's declarations on Iran, saying "administration officials seem to be conditioning the American public not to expect a military strike."

The group recommended sharper public rhetoric that would leave no doubt about Washington's readiness to use force and then to flex US military muscle in the region to drive home the point.

The US military should preposition supplies, carry out exercises with Gulf allies and deploy additional ships -- including minesweepers and an additional aircraft carrier battle group -- to the Gulf and off Oman's coast, it said.

The US Navy already has a substantial presence in the Gulf, with two aircraft carriers often deployed.

The task force called for expanding arms sales to Gulf allies, including more "offensive" weapons, while seeking a "strategic partnership" with Azerbaijan on Iran's border.

Although the report did not advocate Israel taking pre-emptive military action, it said the United States should do more to make Israel's threat credible.

The group urged providing Israel with more advanced bunker buster bombs, which are designed to penetrate underground sites, as well as to supply two to three mid-air refueling tanker aircraft to extend the range of Israeli aircraft in any air raid.

The authors acknowledged a myriad of grave risks in the case of US or Israeli military action, including casualties, rallying Iranians around the regime, retaliation against US and allied targets, a possible temporary closure of the Strait of Hormuz and a spike in oil prices.

But the report argues the United States had to be prepared to use force because the long-term dangers posed by a nuclear-armed Iran outweighed the short-term fallout come from military strikes.