A day after United States Ambassador to India David C Mulford said India has to support the US on the Iran nuclear issue or forget the civilian nuclear deal, the Left parties on Thursday demanded that the United Progressive Alliance government come out with a clear statement that India will not favour any United Nations Security Council referral of Iran's controversial nuclear programme.

"Two things are immediately required if the Manmohan Singh [Images] government is to restore its credibility in this matter. First, there should be a categorical statement that India will not countenance a reference to the UNSC on the Iran nuclear issue.

• Complete Coverage: The Indo-US nuclear tango

"Second, the government should make public all the details of the proposals for nuclear cooperation and the separation of civilian and nuclear facilities, which have been submitted to the US," the Communist Party of India-Marxist said in a statement.

Just a week ahead of the International Atomic Energy Association meeting on the Iran issue, Mulford told PTI in an interview on Wednesday that if India did not vote against Tehran's nuclear programme, the fallout on the Indo-US nuclear deal in the Congress would be 'devastating'.

The CPI-M called the ambassador's comments a threat and said they confirmed that the US had pressurised India to vote against Iran at the IAEA meeting in September.

"The threat issued by the US ambassador that unless India votes against Iran in the IAEA, the nuclear cooperation deal will not be approved by the US Congress is a serious affront to India and its sovereignty," it said.