Claiming Iran may secretly have resumed efforts to build a nuclear weapon, US Defence Secretary Robert Gates called for intensified international pressure on Tehran and urged Saudi Arabia and other Gulf states to develop a joint air and missile shield to ward off future threats.
Speaking at the Manama Dialogue security conference, Dr Gates insisted multilateral defence co-operation was an "absolute necessity". The region faced a "truculent" leadership in Tehran that was "bent on confrontation with its neighbours and deeply engaged in subverting stability in Iraq and Afghanistan," he claimed.
"Everywhere you turn, it is the policy of Iran to foment instability and chaos, no matter the strategic value or the cost in the blood of innocents - Christians, Jews and Muslims alike," he said.
As well as backing Hizbollah and Hamas, Dr Gates said Tehran was developing medium-range ballistic missiles that are "not particularly cost-effective unless equipped with warheads carrying weapons of mass destruction".
Erecting a joint "protective defensive missile umbrella" would enable the GCC states to reduce the chances of a successful attack, he added.
Dr Gates's hardline statements followed last week's publication of the CIA's National Intelligence Estimate (NIE) on Iran. The report's key conclusion that Tehran had suspended a nuclear weapons programme in 2003 embarrassed President George Bush and led some regional allies to suspect the White House was preparing to take a softer line.
Dr Gates dispelled that notion. "The NIE reports that they (Iran) do continue their nuclear enrichment programme ... It states they do have the mechanisms still in place to restart their programme. And the estimate is explicit that Iran is keeping its options open and could restart its nuclear weapons programme at any time - if it has not done so already."
Addressing the International Institute for Strategic Studies' annual security summit, Dr Gates called for intensified economic, financial and diplomatic pressure on Iran. He added that there were many "opportunities" for the US and like-minded countries to maintain the pressure even if Russia and China blocked a third UN sanctions resolution.
While all options, including military action, remained on the table, the US was "100 per cent focused on diplomatic and economic measures".
Regional governments, friendly or otherwise, should not underestimate US resolve, he warned. "Imperial Germany, imperial Japan, Nazi Germany, fascist Italy, the Soviet Union - all made this fatal miscalculation. All paid the price. All are on the ash heap of history."
Regional experts say Gulf leaders share US concerns about Iran's political and nuclear ambitions and speak forcefully about them in private.
But Dr Gates's reassertion of Washington's tough stance, coupled with an ongoing refusal to pursue unconditional talks with Tehran, drew sharp public criticism at the weekend.
Qatar's Prime Minister Shaikh Hamad bin Jassim bin Jabr Al Thani said: "We can't solve our problems by trying to seal Iran off from the region ... The US should hold direct talks."
GCC Secretary General Abdul-Rahman Al-Attiyah said: "We believe in dialogue to solve the crisis."
Gary Samore, of the US Council on Foreign Relations, said the criticisms reflected worries about US intentions. "Gates had to reassure them that the US was not giving up on Iran after the NIE."
Dr Gates stressed the partnership between Bahrain and the US is one of complete commitment toward achieving peace and security in the Gulf.
Iran was invited but pulled out of the high-profile conference at the eleventh hour, a decision which was criticised by many representatives who took part.
Bahrain, however, is also constantly seeking strong ties with Iran, said Crown Prince and BDF Commander-in-Chief Shaikh Salman bin Hamad Al Khalifa.
"We wish that they would have participated in the conference," he said.