Every time it looks as if the big powers have finally run out of patience with Iran's nuclear misdeeds, Tehran's leaders suddenly decide they're in the mood to compromise. And every time the big powers let up on the pressure, Tehran's compromises turn to smoke.

It was no surprise on Monday when Iran announced it was ready to accept a deal to ship some of its nuclear fuel out of the country — similar to the deal it accepted and then rejected last year. So it is welcome news that the United States, Europe, Russia and China will press ahead with new United Nations Security Council sanctions.

The deal to exchange enriched uranium — which could, with more enrichment, be used in a weapon — for fuel rods is worth pursuing. We also are sure that there is no chance of reining in Iran's nuclear ambitions without sustained unified pressure by the major powers.

The resolution, circulated late on Tuesday, takes aim at Iran's financial institutions, including those supporting the Islamic Revolutionary Guards Corps, which runs much of the nuclear program. It would also require countries to inspect ships or aircraft into or out of Iran if there are suspicions they are carrying banned materials.

Like the three resolutions that preceded it, it is probably not tough enough to change minds in Tehran. But the fact that Russia and China — Iran's longtime enablers — have signed on is likely to make some players in Iran's embattled government nervous. (We know we can't wait to hear what changed Beijing's mind.)

Several European governments have signaled that they are ready to impose tougher bilateral sanctions after the Security Council moves, and that might unsettle Iran's shaky political and economic system even more.

Since 2006, Tehran has defied repeated demands from the Security Council to curb its nuclear program. It continues to churn out more nuclear fuel, block international inspectors from visiting suspect nuclear sites and refuses to answer questions about possible research into weapons designs.

The 11th-hour agreement announced this week with the leaders of Brazil and Turkey was much like one reached with the big powers last fall. Iran would transfer about 2,640 pounds of its low-enriched uranium to Turkey within one month and receive — within one year — fuel rods for use in a medical research reactor.

There are big differences, however. In October, 2,640 pounds represented nearly 80 percent of Iran's stock of enriched uranium. Now it is only about half of its supply.

The original deal was intended to measurably delay Iran's progress toward a nuclear weapon while opening the door to serious negotiations. The current deal leaves Iran with too much fuel, puts no brakes on enrichment at a higher rate, lets Tehran take back the fuel stored in Turkey when it wants and makes no commitment to talks.

Brazil and Turkey — both currently hold seats on the Security Council — are eager to play larger international roles. And they are eager to avoid a conflict with Iran. We respect those desires. But like pretty much everyone else, they got played by Tehran.

American officials have not rejected the deal completely. They say that Iran will have to do more to slow its nuclear progress and demonstrate its interest in negotiating, rather than just manipulating the international community.

Brazil and Turkey should join the other major players and vote for the Security Council resolution. Even before that, they should go back to Tehran and press the mullahs to make a credible compromise and begin serious negotiations.