Since President Obama took office, the major powers have imposed increasingly strong sanctions aimed at Iran’s banks and oil trade. It is crucial to maintain that cohesion as a second round of negotiations opens this week in Baghdad.

The initial talks in Istanbul last month were encouraging enough for both sides to agree to meet again. This time, Iran will have to offer concrete proposals to address core concerns. It could move significantly toward a solution by suspending all its uranium enrichment activities, which the United Nations Security Council first demanded in 2006. At a minimum, it needs to stop enriching to 20 percent purity (well beyond the 5 percent needed for civilian nuclear programs and a few steps from bomb grade) and to close its Fordo nuclear facility. If Iran does that, the United States and its allies — Britain, France, Germany, Russia and China — are expected to offer to take the stockpile of 20 percent enriched uranium out of the country, fabricate it into fuel rods for Tehran’s medical research reactor and help with safety upgrades to Iran’s civilian nuclear program.

What the Iranians really want, however, is an end to the sanctions, which are wreaking havoc on the economy. They may show just enough flexibility to encourage Russia and China to push to ease punishments prematurely. Tehran has played that game many times before, while plowing ahead with its nuclear program.

If Iran makes credible gestures, sanctions should be eased, but not significantly until it takes irreversible steps to roll back its nuclear activities. The international community must make that clear before the Iranians start making promises.