But Mr. Ahmadinejad, whose stewardship of the economy has been increasingly challenged by other Iranian politicians in the last year of his term, offered no new solutions to arrest the slide in the rial, which is a major inflationary threat and has become the most visible barometer of Iran’s economic travails. Because of the sanctions, Iran is facing extreme difficulties in selling oil, its main export, and in repatriating dollars and other foreign currencies, because Iran has been cut off from the global banking system.

Unscripted protests in Iran are highly unusual, particularly since the political opposition in the country was crushed after Mr. Ahmadinejad’s disputed re-election in 2009. Iran experts said the outbreak on Wednesday was significant because it appeared to offer an insight into the degree of public weariness.

“It may not be widespread yet, but it demonstrates not just unhappiness with the Ahmadinejad government, but also dissatisfaction with the Islamic republic’s failure to stem the economic crisis brought about by incompetence, mismanagement and sanctions,” said Alireza Nader, a political analyst at the RAND Corporation, a research and consulting firm. He said that “the regime is going to face much greater instability in the future, especially if it loses the support of Iran’s business and merchant class.”

Gary Hufbauer, a senior fellow at the Peterson Institute for International Economics in Washington, said in an audio commentary on the group’s Web site that the sanctions had effectively halved Iran’s oil exports, choked its ability to import essential goods and left its currency worth a fraction of its value compared with early this year. “These are hard times for ordinary and upper-class Iranian people,” he said.

The unrest caught the attention of Secretary of State Hillary Rodham Clinton, who, speaking from Washington rejected Mr. Ahmadinejad’s explanation for the rial’s plunge. She suggested that conditions would improve if Iran engaged in meaningful negotiations over its nuclear program, which Western powers and Israel suspect is meant to develop nuclear weapons, but which Iran says is for peaceful purposes.