Washington has condemned this assault on all traces of reform-minded opposition and free expression. It has sensibly done so in measured tones, not wanting to give Mr. Ahmadinejad another excuse to claim that his opponents are agents of the West, and specifically the United States. Predictably, he has done so anyway.

The viciousness of the current repression is another sign of the government’s desperation. But that is no consolation to Iranians at the receiving end of the terror. Washington is rightly increasing its already substantial efforts to make accurate, uncensored information more widely available through satellite television, radio broadcasts and Internet sites. Last month, Congress authorized $50 million to be spent over the next year on expanded programming, increased transmissions and anti-jamming technology. An America that stands up for its own values of free, uncensored expression need not worry about the epithets a desperate dictator hurls against it.

We believe that the Obama administration was right to reach out to Iran in an effort to curb its nuclear ambitions. But we also believe that there have to be limits to that forthcomingness, and time is running out.

After initially agreeing to send much of its current stockpile of low-enriched uranium abroad for conversion into nuclear reactor fuel, Tehran is now backing away. As long as the centrifuges are spinning, Iran can be expected to drag this on. Mr. Obama has set a deadline of the end of this year for diplomatic progress on the nuclear issue. He should keep to that.

If Iran continues to repudiate the exchange deal  which reduces Iran’s available supply of potential bomb fuel and buys time for further diplomacy  the United States must line up other members of the United Nations Security Council, including Russia and China, for much tougher sanctions.