The European Union’s “unprecedented” oil embargo on Iran began yesterday in what Foreign Secretary William Hague described as the “toughest measures to date”, following stalled talks with Iran at the negotiating table in Moscow last week.

EU countries are imposing a crude oil ban on the Middle Eastern country, as well as a ban on providing financial services related to the sale, purchase and transport of oil.

The sanctions are designed to reign in Iran’s nuclear programme, which Western nations are concerned could be a cover for producing nuclear weapons, a claim the country disputes.

The US introduced similar tough sanctions on Iran on 28 June.

The Foreign Secretary said yesterday: “Today unprecedented oil sanctions on Iran have come into force. These are the toughest measures the EU has adopted against Iran to date. They signal our clear determination to intensify the peaceful diplomatic pressure on the Iranian government.

“Over the course of the next few weeks Iran faces a choice: it can continue to obfuscate and avoid the critical issues, incurring tough sanctions and increasing international isolation. Or it can begin to cooperate seriously by discussing the steps it is prepared to take on its nuclear programme”.

Mr Hague echoed his warning to the country last week, adding that “pressure will only increase” the longer Iran stalls on co-operation.

However Iran claims it has built up $150billion (£96bn) in oil reserves to counter the sanctions, according to Iran’s Mehr News Agency, quoting the chief of Iran’s central bank Mahmoud Bahmani yesterday.