China’s relationship with the US will be determined by how it responds to Iran’s nuclear programme, a senior Bush administration official warned on Wednesday as Washington continued to press Beijing and Moscow to back a tough UN Security Council resolution against Tehran.

Robert Zoellick, deputy secretary of state, elevated Iran’s alleged nuclear weapons development to the single most important issue at stake in US-China relations rather than the usual concerns over the strength of China’s currency and its ballooning trade surplus.

Although less blunt, Mr Zoellick’s prepared remarks on China mirrored those voiced by Dick Cheney, US vice-president, towards Russia last week when he berated Moscow for using its oil and gas as a tool of blackmail and intimidation on the international stage.

Speaking to the House international relations committee, Mr Zoellick said the US acknowledged China’s need for access to energy resources but that it had urged China to use its oil and gas investments in Iran, Sudan and Burma as a lever for the international good, rather than narrow national interests.

He described China’s next move on Iran as “exhibit A” and “critical” in its relationship with the US, which he said was “going to be determined by how they act in Iran in dealing with this nuclear issue”.

Condoleezza Rice, secretary of state, returned to Washington on Wednesday having failed to persuade the foreign ministers of China and Russia to support a Security Council resolution that would require Iran to stop its uranium enrichment programme.

Instead, the US was pushed into backing a UK proposal it had rejected two months earlier, endorsing a plan for the EU3 of France, Germany and the UK to come up with an enhanced package of “benefits” in a new effort to change Iran’s mind. “What was shot down in flames is now a possibility,” one diplomat said.

Ms Rice met Javier Solana, the European Union foreign policy chief, on Wednesday and gave the EU effort two weeks. She pledged there would still be “action” at the UN. The new package had to exclude uranium reprocessing and enrichment, Ms Rice said.

European negotiators are concerned that the tougher US line towards Russia – and now apparently China – will jeopardise their efforts to keep the international coalition on Iran as broad as possible.

Mr Zoellick balanced his warnings to China by stressing the importance of engagement and the need for China as a “responsible stakeholder” in the international system. He said he had sensed that “China will not be an obstacle” regarding Iran.