Two recent diplomatic ventures have raised speculation about a possible back channel between Washington and Tehran. Last week, Jeffrey Feltman, a high State Department official in President Obama’s first term who is now a senior envoy at the United Nations, visited Iran to meet with the new foreign minister, Mohammad Javad Zarif, and discussed possible reactions to an American airstrike in Syria.

At the same time, the sultan of Oman, who has often served as an intermediary between the United States and Iran, was in Tehran meeting with Iran’s supreme leader, Ayatollah Ali Khamenei.

Neither Mr. Feltman nor Sultan Qaboos bin Said al Said of Oman has said anything about carrying messages between the two governments. Still, those overtures, along with some surprisingly mild noises from Iranian leaders, have raised hopes that Washington may be able to thread the needle — to strike Syria without compromising efforts toward an Iranian-American détente before meetings at the United Nations General Assembly this month.