BAGHDAD:Talks between Iran and six world powers snagged Wednesday over dueling proposals concerning Tehran’s nuclear program, a tug-of-war that pits international concerns about the Islamic Republic’s potential to build atomic weapons against enforcing crippling sanctions on its people.

The daylong back-and-forth in Baghdad focused largely on whether the current enrichment level of Iran’s uranium production is a red line the US and other powers will not permit for fear it could become warhead-grade material.

At stake is the threat an Iran armed with nuclear weapons could pose to its neighbors. The US and Israel have indicated readiness to attack Iran if diplomacy and sanctions fail to curb its nuclear program. Both suspect that Iran is aiming to build nuclear weapons, and Israel believes it would be a prime target.

Iran insists its nuclear program is peaceful.

The impasse threatened to dissolve the most hopeful chance of detente in nearly a decade, although both sides agreed to continue negotiations into Thursday.

“The international community hasn’t done something wrong here, we haven’t created a suspicious nuclear weapons program that the world doesn’t know the answers to. Iran has,” a senior US official said early Thursday after the grueling day of discussions that, at times, appeared on the verge of breaking down. “They are the party who has acted to create concerns in the international community.”

However, the official said, the negotiations remain in the beginning of a careful and drawn-out process.

“We certainly are not at the end of it,” said the US official who spoke on condition of anonymity to discuss the talks more candidly.

Western negotiators presented a package Wednesday that called on Tehran to place a freeze on its enrichment of uranium to 20 per cent, considered a short technical step away from bomb grade. In exchange they offered benefits, including medical isotopes, some nuclear safety cooperation and spare parts for civilian airliners, much needed in Iran.

But they snubbed Iranian calls for an immediate easing of significant economic sanctions imposed on Tehran for flouting UN Security Council resolutions that demand the suspension of all enrichment.

Iran brought a potent bargaining chip to the table, tentatively agreeing on the eve of the negotiations to allow UN inspectors into a military complex suspected of conducting nuclear arms-related tests.

The gesture was seen as an attempt to head off painful July 1 sanctions on its oil exports to lucrative European markets. US and European measures have targeted Iran’s oil exports, its chief revenue source, and effectively blocked the country from international banking networks.

Diplomats from the six world powers have refused to consider postponing the new harsher sanctions, although the US official said some restrictions could be removed as part of an agreement.

The talks are seen only as a small step forward in a delicate negotiating process that likely will unfold over months. That would likely bring objections from Israel, which claims that Iran is only trying to buy time to keep its nuclear fuel labs in full operation.

But a delay could allow US and European allies to tone down threats of military action, despite calls Wednesday from a hawkish alliance of US senators who urged negotiators to take a hard line against Iran “to leave no doubt that the window for diplomacy is closing.”

“The Iranian regime’s long record of deceit and defiance should make us extremely cautious about its willingness to engage in good-faith diplomacy,” Republican Senator John McCain and Lindsey Graham, and Independent Joe Lieberman, wrote in Wednesday’s editions of The Wall Street Journal.

“The US must be prepared, if necessary, to use military force to stop Iran from getting a nuclear-weapons capability.”

The Baghdad meetings opened with the so-called 5+1 group, the permanent UN Security Council members, the United States, Russia, China, Britain and France, plus Germany, putting forward a proposal aimed at putting a cap on Iran's growing stockpile of uranium enriched to 20 per cent.

Iran says the uranium is for fuel for medical reactors, but Western diplomats say Tehran already has many times more than it needs, and that moving from 20 per cent to bomb-grade purity is a relatively quick and easy process.

The US official said it is too early in the negotiations to discuss whether world powers would agree to let Tehran maintain a lesser percentage of uranium enrichment. ''It’s premature to have that discussion,'' the official said.

Mike Mann, spokesman for the head of the European Union delegation that is leading the talks, suggested that any rollback in sanctions was unlikely in the Baghdad talks. He called the upcoming sanctions a “matter of the law and they will come into force when they come into force.”

Iran offered a counterproposal that includes “nuclear and non-nuclear issues,” according to the member.