'It hit the defined target,' state television reported, without giving further details.
The two-stage Sejil, powered by solid fuel, is capable of travelling 2,000km, which would put many countries in the region within range.
British Prime Minister Gordon Brown said the test of the missile was a matter of 'serious concern' and makes the case for 'moving further on sanctions.'
Mr Brown is in Copenhagen for the United Nations climate summit, where he discussed the development with UN Secretary General Ban Ki-moon.
'I have expressed to him and he has also expressed concern about the test of a long-range missile by Iran,' Brown said, according to his Downing Street office in London.
'This is a matter of serious concern to the international community and it does make the case for us moving further on sanctions.
'We will treat this with the seriousness it deserves.'
Iran is under three sets of UN sanctions for its refusal to suspend enrichment and risks a further round after rejecting a UN-brokered deal to send its low enriched uranium abroad to be further refined into fuel for a research reactor.
Enrichment lies at the heart of fears over Iran's controversial atomic work as the process to make nuclear fuel can also be used to make the fissile core of an atom bomb in much higher purifications. Iran strenuously denies that its programme is for military use.
The US House of Representatives yesterday overwhelmingly approved sanctions legislation aimed at forcing Iran to freeze the programme by depriving the Islamic republic of petrol.
The measure would empower US President Barack Obama to effectively block firms that supply Iran with refined petroleum products, or the ability to import or produce them at home, from doing business in the United States.
