British Prime Minister David Cameron warned that the "whole world" would take action if Iran closed the strategic Strait of Hormuz, in a television interview during a visit to Saudi Arabia on Friday.
"It is in the interests of the whole world that those straits are open and, if there was any threat to close them, I am sure the whole world would come together and make sure they stayed open," Cameron told Al-Arabiya television.
Cameron's first visit as premier to OPEC kingpin Saudi Arabia comes as Western governments move to step up sanctions over Iran's controversial nuclear programme, threatening an embargo on its oil exports.
The move has drawn an angry response from Tehran which has in turn threatened to shut the strait -- a chokepoint for a fifth of the world's sea-borne oil exports -- if it is attacked or heavy sanctions are imposed.
The New York Times reported late on Thursday that the United States has used a secret channel to warn Iran's leaders against closing the Strait of Hormuz, saying that doing so would provoke a US response.
Cameron also called for a UN Security Council resolution on Syria, where the United Nations estimates an uprising has left more than 5,000 dead since March in a crackdown on protests against President Bashar al-Assad's regime.
"We stand ready as a permanent member of the UN Security Council to take a fresh resolution to that Council, based on what the Arab League is doing and saying," the prime minister said.
He said any party which vetoed, in apparent reference to Russia, would have to "try to explain why they are willing to stand by and watch such appalling bloodshed by someone who has turned into such an appalling dictator."
UN chief Ban Ki-moon, who was in Lebanon on Friday, made a similar appeal, urging the international community to stand together to address the crisis in Syria.
But Russian Deputy Foreign Minister Gennady Gatilov has rejected Western-proposed amendments to a draft Security Council resolution that Moscow circulated last month also calling for a halt to violence by the opposition.
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Western leaders have repeatedly called for the embattled Assad to step down but Moscow has steadfastly stuck by its ally Damascus.
During talks in the Saudi capital, Cameron and King Abdullah "discussed the importance of the UK-Saudi bilateral relationship and agreed to strengthen cooperation in a range of areas," Cameron's office said in a statement.
They "also discussed recent developments in the region, in particular their shared concerns about the situation in Syria, Iran and Yemen," it added.
Yemen has been rocked by a year of unrest in which hundreds have been killed amid fears of a growing Al-Qaeda influence across its southern and eastern provinces due to a weakening central government.
"The prime minister also raised our concerns about Somalia and the problems of conflict, piracy and terrorism which threaten Somalis and the wider international community," Cameron's office said.
"He briefed the king on the aims of next month's London Conference on Somalia, in particular to catalyse a coordinated international effort focused on practical measures to help Somalis rebuild their country."
Somalia has been without an effective central government since president Siad Barre was ousted in 1991 as violence, piracy and famine tear the African country.
Saudi state news agency SPA reported earlier that the two leaders discussed "regional and international developments as well as the various means of strengthening cooperation between both countries," without elaborating.
The meeting was attended by top Saudi officials.
Britain has been seeking to strengthen ties with oil-rich Saudi Arabia, a major market for Western arms deals, and boost exports to its largest Middle East trading partner.
Annual bilateral trade is worth 15 billion pounds ($23 billion), while Saudi investments in Britain amount to more than 62 billion pounds.