The United States and European Union have also approved their own measures, which go further than the UN resolution.

Hugo Chavez, the Venezuelan president, has defended Iran's nuclear programme as "peaceful" and condemned the UN sanctions resolution. His Iranian counterpart, Mahmoud Ahmadinejad, thanked him for his support earlier this week, according to Iran's ISNA news agency.

Iran's falling imports

Venezuela's promise offers symbolic support for Iran, but its practical impact is likely to be limited.

Iran is the world's fifth-largest exporter of crude oil, but refining shortages force it to import much of its gasoline. The country's imports have plunged this summer, though, from 120,000 barrels per day in May to roughly 60,000 today. Energy analysts attribute the drop to international sanctions.

Caracas currently exports roughly 20,000 barrels of gasoline per day to Iran, hardly enough to meet Iran's demands.

It also suffers its own refining shortages, and has been forced to import oil products this year because of outages in its refinery network.

The UN sanctions, which were approved overwhelmingly in June, do not target the energy industry. But the US and EU sanctions do: They penalise companies that invest in Iran's energy sector, or that export refined petroleum products to Tehran.