US Deputy Secretary of State Robert Zoellick told a Congress committee that Chinese officials had made it clear "they agree in principle: they don't want Iran to have a nuclear weapon and they understand the danger of that process."

Zoellick added that Chinese officials had told Washington there may be differences over the tactics to be used because they were worried about "energy security issues", as Iran is a key international oil supplier.

China has joined Russia, among the major powers on the UN Security Council, in opposing talk of sanctions against Iran.

The United States, Britain and France want a UN resolution under Chapter 7 of the UN Charter that would give a warning and follow this with a threat of economic sanctions, and if necessary military action.

But Zoellick told the House of Representatives foreign affairs committee: "If we can bring Russia along with some of this, my own sense is that China will not be an obstacle in the process."

He added that Beijing recognizes that the Iran dispute is "a very important issue in the US-China relationship. We need to keep stressing that."

Zoellick emphasized that China has "shown some cooperation" in increasing pressure on Iran over the nuclear programme which Washington and its allies believe camouflages efforts to build an atomic bomb.

China voted for an International Atomic Energy Agency (IAEA) board decision to report Iran to the UN Security Council.

"They joined the rest of the Security Council on March 29 in adopting the presidential statement" which set a deadline for Iran to meet IAEA demands, said Zoellick.

"They have sent senior officials to Iran, and they've reported back to us, and we have a sense of the message that they're trying to deliver."

Zoellick said Russia and China were hesitant because Chapter 7 "suggests to some the possibility of a use of force".

"They want to be willing to ratchet up the pressure, but they're worried about that aspect," the US official said. "In part because of some of their own history, they get worried about the use of sanctions as you move forward."