A US think-tank that closely tracks Iran's nuclear programme warned the time Iran would need to produce enough weapons-grade material for a bomb was getting shorter.
The Institute for Science and International Security (ISIS) estimated that Iran could now produce enough weapons-grade uranium for one bomb, about 25 kg, in as little as about 1-1.6 months, if it used all its 20% stockpile.
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Additional time would be required to make the actual nuclear weapon but such work would likely be carried out at secret sites and would be difficult to detect, it said in a report.
"The most practical strategy to prevent Iran from obtaining nuclear weapons is to prevent it from accumulating sufficient nuclear explosive material, particularly in secret or without adequate warning," ISIS said.
"The shortening breakout times have implications for any negotiation with Iran," it said on Thursday.
Inspectors from the International Atomic Energy Agency are believed to visit Iran's enrichment facilities about once a week. The UN agency, based in Vienna, said it had no comment on Hosseini's remarks for now. Diplomats accredited to the IAEA said they were not aware of any halt of higher-level enrichment.
Iranian MPs have in the past made statements about Iran's nuclear programme that the government later denied.
While members of parliament's national security commission are regularly briefed on the nuclear programme, they are not directly involved in policy-making. The big decisions are made by Supreme Leader Ayatollah Ali Khamenei.
Western officials have said Iran must stop enriching uranium to 20%, increase the transparency of its nuclear programme, reduce its uranium stockpiles and take other steps to reassure the world that it is not seeking nuclear weapons.
Iran and six world powers – the five permanent members of the UN Security Council, plus Germany – emerged from a new round of nuclear negotiations in Geneva last week saying these had been positive and constructive.
The meeting was the first since Iranian President Hassan Rohani came to office in August promising to try to resolve the nuclear dispute and win an easing of sanctions.
Follow-up talks will be held in Geneva on Nov. 7-8.
Tehran denies allegations by Western powers that it is seeking the capability to produce nuclear arms.
'Iran halts most sensitive uranium enrichment work'
Iran has halted its most sensitive uranium enrichment work, a senior Iranian parliamentarian was quoted as saying, a move that would meet a main demand of world powers negotiating with Tehran over its disputed nuclear work.
Any such development would be a big surprise however, as Western experts believe Iran would want to use its higher-grade enrichment as a bargaining chip to win relief from stringent sanctions which have mangled the Iranian economy.
Iran's enrichment of uranium to levels of 20% is sensitive as it is a relatively short technical step to increase that to the 90% needed for making a nuclear warhead.
Hossein Naqavi Hosseini, a senior member of the parliamentary national security commission, said Iran had stopped enriching uranium above the 5% required for civilian power stations as it already had all the 20% enriched fuel it needs for a medical research reactor in Tehran.
"Enrichment over five percent depends on the needs of the country; Iran's nuclear industry requires 20% enrichment for providing the fuel for its Tehran reactor, but this site has its required fuel at the moment and there is no need for further production," parliament's website quoted Hosseini as saying.
"Tehran will decide whether to have over 5% enrichment or not itself, but the issue of suspension or halt of enrichment activities is meaningless because no production is taking place at the moment," he said.
Iran's production and stockpile of 20% uranium is closely watched in the West and Israel.
The Jewish state, believed to be the only nuclear-armed power in the Middle East, has suggested it could launch military strikes if Iran acquired enough of the material for one bomb, but Iran has kept its 20% stockpile below that level.
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