Iranian President Mahmoud Ahmadinejad has blamed the "enemies" of his country for the sharp falls in its currency, the rial. The currency has fallen to fresh record lows against the US dollar. Iranian Industry Minister Mehdi Ghazanfari has blamed speculators for the fall. But US officials say the slide reflects the success of US economic sanctions targeted at Iran's controversial nuclear programme. Mr Ahmadinejad said Western sanctions amounted to an economic war, but they would not stop the country's programme. "We are not people to retreat on the nuclear issue," he told a news conference in Tehran. "If somebody thinks they can pressure Iran, they are certainly wrong and they must correct their behaviour." The central bank has placed a $5,000 (Â£3,100) limit on the amount of foreign currency travellers can take in or out of Iran. The rial has reportedly lost more than 80% of its value since 2011 because of US-led trade sanctions. Reports from Tehran suggest the rial plunged 18% in Monday's trading and then another 9% on Tuesday. Since the start of the year, the currency has lost four-fifths of its value, says the BBC's Mark Gregory. 'Security move' The US-led sanctions are being imposed on Iran because of the country's disputed nuclear programme. The US accuses Iran of aiming to build nuclear weapons, while Iran counters that it simply wishes to develop nuclear power stations. The sanctions, which are backed by the European Union, include a ban on the purchase of Iranian oil. The US has also threatened to take action against foreign firms and institutions dealing with the Iranian central bank. While Iranians are said to be scrambling to convert their rials into hard currency, thereby adding to the downward pressure on the rial, the government has blamed speculation by money changers. According to the Iranian Fars news agency, Mr Ghazanfari said: "We have greater expectations that the security services will control the branches and sources of disruption in the exchange market. "Brokers in the market are also pursuing the increase in price, because for them it will be profitable, and there is nobody to control them." On Tuesday, the rial was said to be trading in Iran at about 37,500 to the dollar, down from about 34,200 late on Monday. The rial is not traded on the global currency markets, so it is not possible to produce accurate figures for its value. The weakness of the rial has harmed the wider Iranian economy, as it means the country cannot afford to import as many foreign goods and raw materials which are priced in hard currency. BBC News - Iran rial: Mahmoud Ahmadinejad blames slide on 'enemies'