Iran's pursuit of a nuclear weapon continues to pose the greatest diplomatic challenge to the Obama administration and developments this past week were both significant and mixed.

The U.S. announced Tuesday that it had reached a deal with Russia and China on new, tougher sanctions to put the squeeze on Iran. Perhaps the leaders of these nations are finally recognizing that they cannot bet on remaining isolated from the world crisis that could erupt if Iran develops, or even gets close to developing, a nuclear weapon.

Israel has made it clear it cannot tolerate a nuclear-armed Iran. If sanctions do not work, it will act militarily, setting off a chain reaction of events impossible to predict and perhaps to control.

Russian and Chinese support are necessary to pass a United Nations resolution. The sanctions deal reportedly includes: interdiction of Iranian shipments suspected of transporting banned items; blocking financial transactions linked to proliferation efforts; severe limits on arms sales to Iran; and travel bans on senior Iranian officials.

Compromises watered down the sanctions. The Obama administration sought tougher policies to hit Iran's energy-based economy and blacklist its central bank. But the deal she did get was impressive work by Secretary of State Hillary Clinton.

The bad news came earlier in the week when Turkey and Brazil reached an agreement for Iran to ship much of its fuel outside its borders for enrichment. The deal ostensibly would allow Iran to pursue peaceful nuclear power, rather than use the enrichment process for weaponry. Many observers, however, saw it as an attempt by Iranian President Mahmoud Ahmadinejad to seek diplomatic cover while continuing a clandestine nuclear weapons program.

It was troubling to see two U.S. allies defy American wishes by cooperating with Iran. It demonstrates the Obama administration has much diplomatic work left to do.