Iran and Austrian energy group OMV have come together in a major agreement to help develop the country's vast gas resources and build a plant for liquefied natural gas (LNG), official Iranian media said.

State television described it as Iran's biggest such contract with Europe, and some Iranian media put its total value at up to $30 billion over 25 years, including the sale of billions of cubic metres of natural gas to the continent.

But OMV made clear the deal was still at an early stage and did not give any figures, suggesting it had so far only signed a non-binding memorandum of understanding, said a report in the Gulf Times.

It comes at a time of escalating tension between the West and Iran over Tehran's disputed nuclear programme. The US, which accuses Iran of seeking to build atom bombs, has urged its allies not to invest in the Islamic Republic.

Iran sits atop the world's second-largest gas reserves after Russia. But politics, sanctions and construction delays have slowed its gas development and analysts say it is unlikely to become a major exporter for a decade.

The huge reserves are a strong magnet for international energy companies despite the political risks.