MOSCOW (AP) — Iran became more adamant Monday that the world must remove the sanctions that are choking off its oil sales before it will curb activities that could be used to make nuclear weapons, diplomats said. The development dampened hopes that talks this week in Moscow could bridge the gaps between the two sides.

The diplomats said the Islamic Republic had asked the six world powers it is meeting in Moscow for discussions of “comprehensive sanctions relief” along with any consideration of their request that Tehran stop enriching uranium to a level that is just steps away from the purity needed to arm nuclear missiles.

The talks ended Monday with little progress, and slim hopes of a breakthrough when the sides meet again on Tuesday.

“We had an intense and tough exchange of views,” said EU foreign policy spokesperson Michael Mann, according to Reuters.

The United States and others suspect that Iran is enriching uranium to develop nuclear weapons. Tehran denies this, saying all of its nuclear goals are peaceful. But fears have been fueled by Tehran’s refusal to stop enriching or accept uranium from abroad.

The diplomats spoke to The Associated Press as talks between Iran and the six nations — the US, France, Russia, China, Britain and Germany — meant to reduce international concern about Tehran’s nuclear intentions broke for lunch. They said the morning session was inconclusive, with the sides no closer to agreement than at their last session in May in Baghdad, which ended with them far apart.

The six had hoped that Iranian chief negotiator Saeed Jalili would respond directly to their demand that his country stop enriching to 20 percent and related requests, said the diplomats, who demanded anonymity because they were not authorized to talk about the closed session. Instead, they said he presented his side’s conditions for meaningful negotiations, including a request for “comprehensive sanctions relief,” they said.

While the Islamic Republic has previously mentioned lifting sanctions or staying pending ones, one of the diplomats said that its request at the closed meeting Monday was the most direct to date. That appeared to reflect the mounting pain for accumulated sanctions, particularly international embargoes on Iran’s oil sales that now are gathering stream.

Diplomats from several nations meeting with Iran in Moscow depict the talks as significant. They say it could be the last in a series and if negotiators fail to make headway in persuading Tehran to stop higher-grade uranium enrichment, it’s unclear if or when new talks would occur.

While Iran wants the other side to recognize its right to enrich and blink first by easing sanctions, the six nations say the onus is on Tehran to show it is ready to compromise.

The talks are being convened by EU foreign policy chief Catherine Ashton, and her spokesman, Mann, said the six were ready to “address the issues” raised by Tehran.

“We hope the Iranians will seriously engage on a set of proposals we put on the table in Baghdad,” he added.

The six formally are only prepared to ease restrictions on airplane parts for Iran’s outmoded, mostly US-produced civilian fleet and are offering technical help with aspects of Iran’s nuclear program that cannot be used for military purposes.

In addition to longer-term UN and other sanctions, Tehran is now being squeezed by the widening international embargo on its oil sales, which make up more than 90 percent of its foreign currency earnings.

Sanctions levied by the US have already cut significantly into exports of Iranian crude from about 2.5 million barrels a day last year to between 1.2 and 1.8 million barrels now, according to estimates by US officials. A European Union embargo on Iranian crude that starts July 1 will tighten the squeeze.

While not budging on lifting existing sanctions or those already decided upon, diplomats familiar with the talks told the AO, however, that the six are also prepared to guarantee that no new UN penalties will be enacted if Tehran shows enough compromise. The diplomats demanded anonymity because that possible offer has not yet been formally made.

For Iran, the main formal demand remains international recognition of its right to enrich and related issues — with increasing emphasis on sanctions relief. Although it is under UN Security Council sanctions for refusing to stop enrichment because of concerns it could use it to arm nuclear missiles, Tehran insists it has a right to do so to for its stated goal of creating reactor fuel and medical isotopes.

The six, in turn, are ready to gloss over the Security Council prohibition of all enrichment and are prepared — for now — to tolerate Iran enriching to low-grades, suitable for nuclear fuel. But they are pressing the Islamic Republic to stop higher enrichment to 20 percent purity because at that level the material can be turned into weapons grade uranium much more quickly.

The six also want Fordo, the underground Iranian facility where most of this enrichment is taking place, shut down and for Iran to ship out its higher-grade stockpile. Fordo is of special concern because it might be impervious to air attacks, a possible last-resort response to any Iranian bomb in the making.

An Iranian delegate, who demanded anonymity because he was not authorized to discuss Iran’s position, told The Associated Press that his country was ready to compromise but only if the six accepted Tehran’s right to enrich, a concession that would effectively nullify the Security Council ban.

In turn, he said that Iran may agree to consider suspending 20 percent level enrichment as a voluntary, temporary measure.

“Our minimum demand … is for them to recognize our right to uranium enrichment,” he said. “If this is not accepted by the other side, then the talks will definitely collapse.”

Iran would be most immediately hurt by a lack of progress in Moscow followed by any long hiatus in new negotiations but the White House also stands to lose.

Failed talks at Moscow with no immediate prospect of new meetings would expose President Barack Obama to criticism of weakness in dealing with Iran from his US Republican presidential challenger Mitt Romney and from Israel, which has threatened to attack the Islamic Republic’s nuclear installations should diplomacy fail.

It is unclear if the Jewish state would actually make good on such a threat. But any military move would likely draw in the US and widen the conflict through much of the Mideast.