Any attempt by Iran to choke off the Strait of Hormuz, a key trading route for the world's oil markets, would be "unsuccessful", the Defence Secretary warned yesterday, adding that British naval forces would continue to help maintain security in the region.

Speaking in Washington, Philip Hammond said attempts to close the waterway, through which a third of the world's oil passes, in retaliation for tougher international sanctions against Tehran, would be illegal. "Disruption to the flow of oil through the Straits of Hormuz would threaten regional and global economic growth," he added.

Mr Hammond said Britain had provided minesweeping vessels as part of the Combined Maritime Forces, the US-led force from 25 states, based in Bahrain. Iran recently carried out naval exercises and fired a sea-to-air missile to emphasise that it could hit back against an attack by the US or Israel.

In response to increased Western pressure, Iran claimed yesterday it could withstand a widening embargo on its oil exports and escalating sanctions directed against its central bank, but said it was ready to resume talks on its uranium enrichment programme.

Like Iraq with its non-existent weapons of mass destruction, Iran would have difficulty proving it does not have secret facilities or plans to develop a nuclear weapon. Iran says its plans are entirely non-military.