A face-off begins this coming week among the world's major powers over whether to impose new economic sanctions to pressure Iran into suspending its nuclear-fuel program.

Weeks of shadow diplomacy will start to gel on Thursday, when the governing board of the International Atomic Energy Agency, the United Nations' nuclear watchdog, meets in Vienna to debate the IAEA's latest report on Iranian cooperation with inspections of its fuel program. Iran says its program is purely civilian. The U.S. and its European allies believe it is for weapons.

The positions of the U.N.'s big powers are already well staked out. The U.S., Britain and France want the U.N. Security Council to impose a third round of much tougher sanctions on Iran. China and Russia are reluctant. Twice already, when Iran failed to meet suspension deadlines, the Security Council has worked out a middle road of relatively low-impact sanctions. This time, as an end-of-month deadline for Iran to suspend enrichment approaches, reaching agreement is likely to be harder.

One reason is that the Security Council's strategy has been questioned lately. That strategy is to pressure Iran to suspend its fuel program, so it can't develop the know-how to make fuel for nuclear warheads even as it negotiates guarantees of the fuel program's peaceful nature. The IAEA's chief, Mohammed ElBaradei, in May said the strategy had become pointless. Iran already has the know-how, he said.

The Egyptian-born diplomat then made his own parallel proposals to Tehran, asking the Iranians to come clean on questions about how its decades-old covert nuclear program was developed. Mr. ElBaradei circulated his progress report on that effort Thursday. It said the Iranians are being more transparent but are still holding back some information and have accelerated their enrichment program.

The common international front on Iran, always shaky, shows growing stress. Russia and China have been angered by U.S. saber-rattling and unilateral sanctions, as well as by threats from France and Britain that Europe could impose unilateral sanctions on Iran's oil and finance industries if the Security Council doesn't act. That Security Council vote is scheduled for December.

China Foreign Minister Yang Jiechi, visiting Tehran earlier this past week, said further sanctions would do "no good." Russian media and trade publications have widely reported that Iran has begun talks to buy more than 200 Russian SU-30 fighter jets and 40 Chinese J-10 aircraft to modernize its obsolete air force. Iran has neither confirmed nor denied the talks. China this past week scuttled a meeting on Iran of senior diplomats from the major powers, scheduled for Monday in Brussels, citing a schedule conflict, according to diplomats familiar with the matter.

"There has been dragging of feet by the Chinese" on a new council resolution, U.S. Ambassador to the U.N. Zalmay Khalilzad told reporters in New York Thursday, warning Beijing that if it blocked further U.N. sanctions, it would be responsible for the failure of diplomacy to rein in Iran's nuclear program.

Awash in oil revenue, Iran appears increasingly confident it can outlast the Western pressure. Tehran didn't even reply to an offer from European Union foreign-policy representative Javier Solana, who negotiates with Iran on behalf of the EU and the Security Council's permanent members, to hold talks this coming week ahead of the next suspension deadline.