Philip Hammond is to warn Iran that any attempt to block the Strait of Hormuz, a vital shipping lane, would be "illegal and unsuccessful" and would be countered militarily if necessary.

The defence secretary is expected to deliver the message in a speech after talks at the Pentagon with his US counterpart Leon Panetta during his first visit to Washington in the role.

He will also defend severe cuts to military spending on both sides of the Atlantic but accuse other Nato countries of failing to pull their weight.

The visit comes amid heightened tensions between Tehran and the US and other allies, fuelled by the implementation of tougher sanctions against the regime.

Iran has threatened to close the Strait of Hormuz over the dispute about its nuclear programme.

"It is in all our interests that the arteries of global trade are kept free, opening and running," Hammond will say in a speech to the Atlantic Council.

"For example, our joint naval presence in the Arabian Gulf, something our regional partners appreciate, is key to keeping the Strait of Hormuz open for international trade.

"The Royal Navy will continue to play a substantial role as part of the Combined Maritime Forces, both at the headquarters in Bahrain, and through our mine counter-measure vessels which help maintain freedom of navigation in the Gulf.

"Disruption to the flow of oil through Strait of Hormuz would threaten regional and global economic growth. Any attempt by Iran to do this would be illegal and unsuccessful."

Echoing recent comments by the head of the UK armed forces, Hammond will also point to the economic crisis as the most serious threat to national and international security.

Countries would have to work together more to reduce the "astronomical" costs of modern warfare, he will say, as deep cuts are implemented on both sides of the Atlantic.

"Without strong economies and stable public finances it is impossible to build and sustain, in the long-term, the military capability required to project power and maintain defence.

"That is why today the debt crisis should be considered the greatest strategic threat to the future security of our nations."

Last month, the head of the British armed forces said the biggest strategic risk facing the UK was economic rather than military.

General Sir David Richards, the Chief of the Defence Staff, said the country's main effort must be the economy, as "no country can defend itself if bankrupt".

Hammond will continue: "The fact is, in this era of austerity... not even the United States can afford the astronomical resource commitment required to deal with every threat from every source.

"In times of economic austerity, fixing these problems will mean finding smarter ways of working together to get greater capability from the resources that exist."

But he will demand a greater contribution from some European allies.

"Libya and Afghanistan have highlighted the significant difficulties we face in ensuring that Nato continues to serve the needs of collective security.

"Too many countries are failing to meet their financial responsibilities to Nato, and so failing to maintain appropriate and proportionate capabilities.

"Too many are opting out of operations or contributing but a fraction of what they should be capable of. This is a European problem, not an American one. And it is a political problem, not a military one."