Despite strong words from Barack Obama and Gordon Brown, there is no sign of a consensus on what additional sanctions should or could be imposed by the international community if Iran continues to ignore concerns about its suspect nuclear programmes. Tehran is meanwhile busy taking pre-emptive measures to mitigate any UN or unilateral punishment, despatching diplomatic missions to China, central Asia and Venezuela and stockpiling petrol and gas in case of winter shortages.

The option preferred by many in the US Congress – a ban on exports to Iran of refined fuel products including petrol – looks like a non-starter. Iran is seen as vulnerable on this front since it imports 40% of its gasoline. But it has the world's second largest proven crude oil reserves and China is the world's second largest crude oil importer. For American hawks this is a marriage made in hell. But no divorce is in prospect.

Iran provided 10% of China's crude oil needs last year; its market share is expected to grow. Chinese companies and middlemen are supplying one third of Iran's refined petroleum requirements as western companies back off. Earlier this year the China National Petroleum Corporation signed a $1.7bn investment deal with the National Iranian Oil Company. The overall Chinese energy stake in Iran is said to be worth $100bn.

Speaking before crucial nuclear talks in Geneva, Chinese foreign ministry spokeswoman Jiang Yu urged the US, Britain and other UN security council members to eschew confrontation. "We believe that all sides should take more steps to ease tensions and resolve problems, not the opposite," she said. Beijing's meaning was plain. Even if it supported sanctions in principle (which it does not), it was not disposed to support measures that would harm its national economic self-interest.

Russia's previous opposition to tougher sanctions appeared to soften last week when its president, Dmitry Medvedev, met Obama in Pittsburgh for a mutual admiration session. But it is unclear what has changed in practice. Moscow views Tehran as an important ally and trading partner in the Caucasus, Caspian and central Asian regions. It is also uncertain whether the youthful Medvedev, rather than his more powerful, less co-operative mentor, Vladimir Putin, is really calling the shots.

Iran's neighbours are reluctant to climb aboard the sanctions bandwagon. Turkey's prime minister, Recep Tayyip Erdogan, said he would discuss the nuclear issue when he met Iran's president, Mahmoud Ahmadinejad, in Tehran next month. But he warned: "Those sanctions won't bring about anything good for the people of Iran. So I think we have to be careful." Even less help can be expected from Iraq, which experienced devastating UN sanctions in the 1990s and whose Shia leadership is closely allied with Tehran; or from Afghanistan, whose government barely controls Kabul's bazaar let alone the smuggling havens along its border with Iran.

As for Pakistan, its president, Asif Ali Zardari, warmly embraced Ahmadinejad in New York last week and said he looked forward to working closely with Iran "to promote peace and security" and improve commercial ties, the Tehran Times reported. "The two presidents also discussed the Iran-Pakistan gas pipeline and the need to step up work on this lucrative project," it said. And how to close off prohibited commercial traffic between Iran and Dubai, a major re-export hub in the Gulf, is another unanswered challenge.

Contemplating these obstacles, US officials are increasingly focusing on curbs on international companies undertaking financial, banking, insurance and investment business on behalf of or in Iran, in addition to US and EU government-level action. Such measures, recalling those used against North Korea, have already persuaded some western energy companies to pull back from Iran. They also have the advantage of not requiring security council approval – a boon if China and Russia block a fourth round of sanctions.

Robert Gates, the US defence secretary, expressed optimism in weekend television interviews that, if need be, Iran could be brought to heel by additional penalties. "There are a variety of options still available," he said; it was "a pretty rich list to pick from". Measures could be enforced that "have the potential to bring them to change their policies", Gates said.

But many profoundly disagree. Writing in the Wall Street Journal, Eliot Cohen, a former Bush administration official, said Gates was kidding himself. "A large sanctions effort has been under way against Iran for some time. It has not worked to curb Tehran's nuclear appetite, and it will not," he said. Sanctions were a mere fig-leaf for weak politicians. And since doing nothing was not an option, Washington's only logical alternative was to "actively seek the overthrow of the Islamic Republic" by whatever means necessary, barring all-out invasion.

With such dangerously ill-considered threats emanating from the world's only nuclear superpower, little wonder Tehran's own hardliners are circling the wagons. And little wonder Beijing, the new voice of reason, is pleading for calm.