UNITED NATIONS — A highly critical report on Iran by the International Atomic Energy Agency last week has led to stepped-up calls from the United States and Europe for a fourth round of U.N. sanctions against Tehran. The West still faces a strenuous battle to win over China, which has insisted on the need for further negotiations aimed at persuading the Islamic republic to place its nuclear program under greater international control.

Here is a guide to the key players among U.N. ambassadors who will be negotiating what Washington hopes will be the fourth round of sanctions.

– Susan E. Rice: United States.

Rice is the only U.N. ambassador who serves in her government’s foreign-policy cabinet, placing her in a unique position to help shape her government’s policy toward Iran. But this will mark her first major role as a negotiator on the Iranian nuclear crisis, pitting her against Russian and Chinese envoys who have traditionally resisted tough sanctions against Iran. Rice will be looking to sanction Iran’s central bank and press for targeted travel and financial restrictions on officials and businesses linked to Iran’s Revolutionary Guard Corps. State Department officials have sought to dial back expectations that Rice would be able to secure support from China and Russia for the kind of “crippling sanctions” the Obama administration once promised. “We are committed to working with other nations to address the very serious dangers posed by Iran’s nuclear program and its failure to meet its international obligations,” Rice said.

– Gérard Araud: France.

France’s former political director oversaw his government’s Iran policy from 2006 until last year and has played a central role in crafting the previous three Iran sanction resolutions.

Now in New York, Araud has been pushing a harder line than the Americans, advocating an expanded arms embargo and sanctions on Iran’s oil revenue. Araud recognizes that any U.N. sanctions resolution that emerges from the Security Council will be weak but that it will provide political cover for tougher sanctions from the United States and Europe. A former French ambassador in Tel Aviv, Araud suspects that Israel may be willing to launch a military strike against Iran if sanctions fail to restrain Iran’s nuclear ambitions. “A military confrontation could not be excluded,” Araud told students last month at Columbia University.

– Li Baodong: China (incoming).