The uprising in Syria, now in its 11th month, has caused extreme discomfort to Hamas, the Palestinian Islamist organization that has been based in Damascus, Syria, for years. Last Friday, Khaled Meshal, Hamas’s leader, left Damascus with no plans to return. Earlier in January, Ismail Haniya, Hamas’s prime minister in Gaza, visited Turkey, a former Assad ally is now perhaps his most powerful regional critic.

It is by no means a certainty that Mr. Assad, who has repeatedly rejected calls for his resignation, will depart soon, despite the increased pressure on him on the streets of Syria and at the United Nations Security Council, where an effort by Western powers and the Arab League is under way to force him aside.

But as signs of his unpopularity have spread in Syria and his list of supporters declines, Iran has been one of the few conspicuous allies of Mr. Assad that has not abandoned him — possibly because it has no alternative. Except for Mr. Assad’s minority Alawite sect, other components of Syria’s fractured sectarian mosaic have no affinity for Iran.

Many Syrians now view Iran as siding with their oppressor. There have been at least three instances in recent weeks of abductions of Iranians in Syria by anti-Assad forces.

The most notable was the seizure last month of five Iranians, whom Iran’s state-run press called engineers but anti-Assad groups said were military advisers. In a video posted online by a unit of the insurgent Free Syrian Army, which claimed to hold the Iranians, one of the men identified as a hostage said the five had been “involved in suppressing and shooting ordinary Syrians,” and urged Ayatollah Ali Khamenei, Iran’s supreme leader, “to order the Iranian military personnel who suppress the Syrians to be repatriated from Syria, so we can also return home.”

While the veracity of that video has not been confirmed, it suggested a level of resentment in Syria toward Iran that had not been seen before.

Iran has continued to publicly recite Mr. Assad’s version of the uprising — that it is terrorism financed by foreign powers hostile to Syria. Ayatollah Khamenei added his voice on Tuesday, denouncing what he called “the interference of America and its allies in Syrian domestic issues.”