Top diplomats from the world’s leading economies increased pressure on Iran on Tuesday over its suspect nuclear programme, but the main audience for the tough talk seems to be a country not represented at the exclusive Group of Eight economic club: China.

Opening a conference of foreign ministers from the eight industrialized nations, Canadian Prime Minister Stephen Harper, said Iran must halt its nuclear enrichment activities and comply with demands to come clean about its atomic programme.

On behalf of the ministers, Mr. Harper urged “a heightened focus and stronger coordinated action, including sanctions if necessary, on the Iranian regime.” He said “Tehran must halt its nuclear enrichment activities and engage in peaceful dialogue.”

He also called on North Korea to return to multinational talks aimed at getting it to abandon nuclear weapons. He said Tuesday’s meeting was being held during “a particularly difficult time” in the international community’s dealings with Iran and North Korea.

“Both are countries whose actions contravene their international obligations,” Mr. Harper said. “Both use violence and intimidation to deprive their citizens’ fundamental rights, both are serious threats to global security.”

With Iran refusing to comply, the message is largely directed at China, a permanent member of the U.N. Security Council that is not a member of the G—8.

China, a vocal opponent of sanctions, wields veto power in the United Nations Security Council, and until recently it had balked at the mere suggestion of taking additional punitive steps against Iran. That, U.S. Secretary of State Hillary Rodham Clinton suggested, is now changing.

In an interview with Canadian television on Monday, Ms. Clinton said China shared the view of the U.S., its European allies and Russia that “a nuclear—armed Iran is not acceptable.”

“I think as the weeks go forward and we begin the hard work of trying to come up with a Security Council resolution, China will be involved, they will be making their suggestions,” she said.

Publicly, China reiterated its stance that the countries should seek a solution through negotiations, not new sanctions.

“We hope relevant parties could fully show their flexibility and make further efforts towards a proper resolution of this issue through diplomatic means,” Chinese Foreign Ministry spokesman Qin Gang, said on Tuesday at a regular news briefing.

China opposes nuclear weapons for Iran, but said the country has the right to peaceful use of nuclear energy.

Iran is already under three sets of U.N. Security Council sanctions and China has been holding up consideration of a fourth, saying diplomacy must be given more time to work. But last week it softened its position in a conference call among senior officials from the six nations working most closely on the matter, according to diplomats.

A senior U.S. official told reporters travelling with Clinton that the Chinese “have said now that they will engage on the elements of a sanctions resolution.” The official spoke on condition of anonymity to discuss an ongoing diplomatic negotiation.

In Washington, meanwhile, the White House said President Barack Obama met on Monday with China’s incoming ambassador to the United States. It said Mr. Obama had stressed to the envoy the need for the two countries “to work together and with the international community on critical global issues including non-proliferation and pursuing sustained and balanced global growth.”

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