The Middle East could be the battleground for a new cold war, if Iran succeeds in acquiring nuclear weapons, Britain's foreign secretary has warned.

William Hague said the world would face the most serious round of nuclear proliferation since the invention of the atomic bomb, which would be a "disaster in world affairs".

Hague's comments come as officials in Washington expressed fears that Iran is ignoring economic sanctions, increasing the likelihood of Israel and or the US attacking the Islamic Republic this year.

Hague insisted that the UK did not currently support military action against Iran but added "all options must remain on the table".

"[The Iranians] are clearly continuing their nuclear weapons programme," Hague told the Daily Telegraph. "If they obtain nuclear weapons capability, then I think other nations across the Middle East will want to develop nuclear weapons.

"And so, the most serious round of nuclear proliferation since nuclear weapons were invented would have begun with all the destabilising effects in the Middle East. And the threat of a new cold war in the Middle East without necessarily all the safety mechanisms. That would be a disaster in world affairs."

Hague's desire to give economic sanctions time to work is reflected in Washington. However, officials in key parts of the Obama administration are increasingly convinced that sanctions will not deter Tehran from pursuing its nuclear programme. They believe the US will be left with no option but to launch an attack on Iran or watch Israel do so.

The president has made clear in public, and in private to Israel, that he is determined to give sufficient time for recent measures to bite deeper into Iran's already battered economy before retreating from its principal strategy to pressure Tehran. These measures include the financial blockade and the looming European oil embargo.

But there is a strong current of opinion within the administration – including in the Pentagon and the state department – that believes sanctions are doomed to fail. They also believe their principal use now is in delaying Israeli military action, as well as reassuring Europe that an attack will only come after other means have been tested.

"The White House wants to see sanctions work. This is not the Bush White House. It does not need another conflict," said an official knowledgeable on Middle East policy. "Its problem is that the guys in Tehran are behaving like sanctions don't matter, like their economy isn't collapsing, like Israel isn't going to do anything.

"Sanctions are all we've got to throw at the problem. If they fail, then it's hard to see how we don't move to the 'in extremis' option."

The White House has said repeatedly that all options are on the table, including the use of force to stop Iran obtaining a nuclear weapon, but that for now the emphasis is firmly on diplomacy and sanctions.

But long-held doubts among US officials about whether the Iranians can be enticed or cajoled into serious negotiations have been reinforced by recent events.

"We don't see a way forward," said one official. "The record shows that there is nothing to work with."

President Mahmoud Ahmadinejad claimed this week that Iran had loaded its first domestically-made fuel rod into a nuclear reactor, and he also threatened to cut oil supplies to six European countries. This was read as further evidence that Tehran remains defiantly committed to its nuclear programme.

If Obama were to conclude that there is no choice but to attack Iran, he is unlikely to order it before the presidential election in November, unless there is an urgent reason to do so. The question is whether the Israelis will hold back that long.

On Friday, the US and EU expressed optimism at the possibility of a resumption of talks with Iran. US secretary of state Hillary Clinton said a letter from Iran to the US and its allies was "one we have been waiting for".

But other US officials complained that the latest Iranian offer to negotiate with the UN security council appeared to contain no significant new concessions. They believed that renewed talks would likely steer discussions away from the nuclear programme.

That view was strengthened by Iran's increasingly belligerent moves such as the botched attempts, which were laid at Tehran's door, to attack Israeli diplomats in Thailand, India and Georgia. Such moves are compounding the sense that Iran is far from ready to negotiate.

Feeding into the considerations are the timing of the US election, including its bearing on Israeli thinking, as well as the pace of Iranian advances in their nuclear programme.

Obama has publicly said that there are no differences with Israel on Iran, describing his administration as in "lock step" with the Jewish state.

But the US and Israel are at odds over the significance of Iran's claim to have begun enriching uranium at the underground facility at Fordow, near the holy city of Qom, and therefore the timing of any military action.

Israel's defence minister, Ehud Barak, has warned that Iran cannot be allowed to establish a "zone of immunity" at Fordow, where it is able to work on a nuclear weapon deep underground and protected from Israel's conventional weapons. Earlier this month, Barak said Israel must consider an attack before that happens.