BEIRUT, Lebanon — For years, allies of the United States across the Middle East have sounded the alarm about Iran’s progress in strengthening their enemies, building up arsenals and sponsoring militant groups near or inside their borders to advance Tehran’s interests.

But since President Trump ordered the drone strike on Friday that killed Maj. Gen. Qassim Suleimani, the mastermind of Iran’s regional efforts, however pleased they might have been, the predominate response from America’s friends in the region has been silence.

This mix of private celebration and public caution reflects two driving fears. Many expect that to avoid a spiral of violence with the United States, Iran could avenge General Suleimani’s death by attacking American allies. And if that happens, many of those allies wonder, will Mr. Trump will have their back?

“The entire region is on edge, as we are in unchartered territory,” said Taufiq Rahim, a senior fellow at the foundation New America who researches politics in the Persian Gulf. “There is no way to be ready for what comes next, because anything could be a target.”