Hammond warns Iran over threat to close oil trade route
Any attempt by Iran to close a vital trade route would fail, Defence Secretary Philip Hammond has told US think tank the Atlantic Council.
In a speech in Washington, he said UK and US forces in the region would stop the closure of the Strait of Hormuz.
He said disrupting the flow of oil would be "illegal and unsuccessful" and threaten regional and global growth.
Iran has threatened to shut the route if sanctions were imposed on its oil exports because of its nuclear plans.
In November, Britain ordered all British financial institutions to stop doing business with their Iranian counterparts, including the country's central bank.
And the UN Security Council has passed four rounds of sanctions against Tehran for refusing to halt uranium enrichment.
Mr Hammond had been visiting the Pentagon for talks with US defence secretary Leon Panetta before delivering his speech.
"It is in all our interests that the arteries of global trade are kept free, open and running," he said.
"For example, our joint naval presence in the Arabian Gulf, something our regional partners very much appreciate, is key to keeping the Straits of Hormuz open for international trade.
"Disruption to the flow of oil through the Straits of Hormuz would threaten regional and global economic growth. Any attempt by Iran to close the Straits would be illegal and unsuccessful."
Iran recently conducted 10 days of exercises near the strategically vital Strait of Hormuz, test-firing several missiles.
Mr Hammond told the Atlantic Council he assumed Iran was working "flat out" to produce a nuclear weapon, but that he would not support a pre-emptive strike on the country.
He said Britain's Royal Navy would continue to play a substantial role in the Combined Maritime Forces, a US-led force based in Bahrain and drawn from 25 nations.
Its mission includes counter-piracy, counter-terrorism and Gulf security.
"We have mine counter-measures capability, we have a frigate present there, and we are an integrated part of the allied naval task force in the Gulf," Mr Hammond added.
"One of the missions of that task force is to ensure that those shipping lanes remain open."
He said Britain would maintain pressure on Iran not to carry on with illegal activities by using nuclear technologies in the "field of military" or by threatening to close international waterways.
But he added: "We also at the same time continue to extend the hand of engagement."
The defence secretary also said that while he was in the US, he would seek reassurances that deep cuts in US military spending would not adversely affect Britain.
President Barack Obama has said a "leaner" force would place a higher priority on Asia and reduce its focus on Europe.
Mr Hammond said he wanted particular commitments on the delivery of US-built strike fighters for the next generation aircraft carriers.
The US has already said it would not tolerate any closure of the Strait of Hormuz.
Britain downgraded ties with Iran in November following an attack on its embassy in Tehran, which Foreign Secretary William Hague has said included "some degree of regime consent".
Britain responded by pulling all of its diplomats out of the country and expelling Iranian diplomats from the UK.