Iran has sparked anger by test-firing an upgraded version of its most advanced missile, which is capable of hitting Israel and parts of Europe.
The action was the latest show of strength aimed at preventing any military strike against it amid the nuclear stand-off with the UN.
The test stoked tensions between Iran and the West, which is pressing Tehran to rein in its nuclear programme.
British Prime Minister Gordon Brown said it showed the need for tougher UN sanctions on Iran.
"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," Mr Brown said after talks with UN chief Ban Ki-Moon in Copenhagen.
Wednesday's test was for the latest version of Iran's longest-range missile, the Sajjil-2, with a range of about 1,200 miles (2,000 kilometres). That range places Israel, Iran's sworn enemy, well within reach - as well as US bases in the Gulf region and parts of south-eastern Europe. The two-stage Sajjil-2 and is powered entirely by solid-fuel while the older, long-range Shahab-3 missile uses a combination of solid and liquid fuel in its most advanced form.
Iran has repeatedly warned it will retaliate if Israel or the US carries out military strikes against its nuclear facilities, at a time when the US and its allies accuse Tehran of seeking to develop a nuclear weapon. Iran denies the claim, saying its programme is intended solely to generate electricity.
Nuclear negotiations have been deadlocked for months, with Iran equivocating over a UN-drafted deal aimed at removing most of its low-enriched uranium from the country so it would not have enough stockpiles to produce a bomb. The UN nuclear watchdog last month sharply rebuked Iran for refusing to halt uranium enrichment.
State television broke the news in a one-sentence report accompanied by a brief clip of the test, showing the missile rising from the launch pad in a cloud of smoke.
Iran's Defence Minister, General Ahmad Vahidi, said the Sajjil-2 would be a "strong deterrent" against any possible foreign attack. He said the new version can be fired more quickly and flies faster than previous ones making it harder to shoot down, though he did not give further details. He told state TV: "Given its high speed, it is impossible to destroy the missile with anti-missile systems because of its radar-evading ability."
