"I have unlimited time, as far as I'm concerned," Donald Trump said on Iran. (File)

U.S. President Donald Trump said on Wednesday that he was "not talking boots on the ground" should he take military action against Iran and that he had "unlimited time" to try to forge an agreement with Tehran.

Iran suggested it was just one day from breaching a limit in the 2015 nuclear deal that restricted its stockpile of uranium, a move that would pressure European countries aiming to be neutral to pick sides.

The fate of the multilateral nuclear deal, under which Iran agreed to curbs on its nuclear program in return for relief from economic sanctions, has been at the heart of the U.S.-Iran dispute which took on a military dimension in recent weeks.

Last week Iran shot down a U.S. drone it said was in its air space, which Washington denied. Trump called off retaliatory air strikes at the last minute, saying too many people would have died. Washington also accused Tehran or its proxies of attacks in May and June on six tankers in the Gulf region, which Iran denies.

Asked on Fox Business Network if a war was brewing, Trump replied: "I hope we don't but we're in a very strong position if something should happen."

"I'm not talking boots on the ground," Trump said. "I'm just saying if something would happen, it wouldn't last very long."

Speaking later at a gathering of religious conservatives, the U.S. president talked about whether there could be a new agreement with Iran, suggesting he could live without one.

"If it doesn't happen, that's fine with me," Trump said. "I have unlimited time, as far as I'm concerned."

Trump last year unilaterally withdrew from the nuclear deal with Iran struck by his predecessor President Barack Obama, arguing that it did not go far enough to restrict Iran's nuclear and missile programs and other activities in the Middle East.

He has since re-imposed U.S. economic sanctions on Iran, including taking the unprecedented step in May of trying to drive Iran's oil exports to zero.

'LITTLE GESTURES TO REDUCE TENSIONS'

Iran warned the U.N. Security Council on Wednesday that it would no longer be burdened with preserving the pact, originally struck by Iran and Britain, China, France, Germany, Russia and the United States. European states pushed Tehran to stick with the agreement because there was no peaceful alternative.

"Iran alone cannot, shall not and will not take all of the burdens any more to preserve the JCPOA," Iran's U.N. Ambassador Majid Takht Ravanchi told the 15-member Security Council, using the acronym for the deal's formal name, the Joint Comprehensive Plan of Action.

U.S. allies warn that an increase in tensions could accidentally lead to war.

Iran and world powers including the United States who struck the nuclear pact needed to find a way back into talks, French President Emmanuel Macron said on Wednesday.

"I believe the escalation, sanctions on top of sanctions, provocations, the military build-up, is extremely dangerous because it could ignite the region, it could lead to over-reactions," he told Japanese broadcaster NHK before a G20 summit in Osaka.

"When confidence is lost, you need little gestures to reduce tensions."

'OBLITERATION'

Although the United States and Iran both say they do not want war, last week's aborted U.S. strikes have been followed by menacing rhetoric on both sides. On Tuesday Trump threatened the "obliteration" of parts of Iran if it struck U.S. interests. President Hassan Rouhani, who normally presents Tehran's mild-mannered face, called White House policy "mentally retarded."

The standoff creates a challenge for Washington which, after quitting the nuclear deal against the advice of European allies, is now seeking their support to force Iran to comply with it.

Over the past few weeks Iran has set a number of deadlines for European countries to protect its economy from the impact of U.S. sanctions or see Tehran reduce compliance with the deal.

A spokesman for Iran's Atomic Energy Organisation said that one of those deadlines would expire on Thursday, with Iran potentially exceeding a limit imposed under the deal to keep its stockpile of enriched uranium below 300 kg.

The IRIB news agency quoted spokesman Behrouz Kamalvindi as saying that after the deadline Iran would speed up its rate of producing the material.

Another threshold bars Iran from enriching uranium to a purity beyond 3.67 percent fissile material. It has set a deadline of July 7 after which it could also breach that.

European nations have tried to save the deal by maintaining some of its economic benefits despite U.S. sanctions. So far they have failed, with Iran largely shut from oil markets and all major European companies cancelling plans to invest.

Senior British, French, German and U.S. diplomats meet in Paris on Thursday, and senior officials from the six nations still in the deal gather in Vienna on Friday for talks that may explore whether the deal can be salvaged through diplomacy.

Iran says it would be Washington's fault if it exceeds the 300 kg stockpile threshold. The 2015 deal allows Iran to sell excess uranium abroad to keep its stockpile below the limit, but such sales have been blocked by U.S. sanctions.