Iran said on Sunday that a person close to the government team that negotiated its nuclear agreement with foreign powers had been arrested on accusations of espionage and released on bail.
The disclosure, reported in the state news media, appeared to be the latest sign of the Iranian leadership’s frustration over the agreement, which has failed so far to yield the significant economic benefits for the country that its advocates had promised. Iranian officials have blamed the United States for that problem.
Despite the relaxations of many sanctions under the accord, which took effect in January, Iran faces enormous obstacles in attracting new investments and moving its own money through the global financial system.
The Iranians are still blocked from using American banks, an important transit point for international capital, because of non-nuclear-related sanctions imposed by the United States.
There were unconfirmed reports last week that the Iranian authorities had arrested Abdolrasoul Dorri Esfahani, who has dual Iranian and Canadian citizenship, on espionage suspicions.
Mr. Esfahani, an adviser to Iran’s central bank, helped the Iranian nuclear negotiators bargain for sanctions relief in exchange for Iran’s pledges of verifiably peaceful nuclear work.
The official Islamic Republic News Agency said a spokesman for Iran’s judiciary, Gholam Hossein Mohseni Ejei, speaking at a weekly news conference on Sunday in Tehran, had “confirmed the arrest of an individual from the negotiating team.”
But the spokesman also said that “his charge of spying has not been proved” and that the suspect had been released on bail pending an investigation.
The spokesman did not identify the suspect by name, which was considered unusual.
He also did not explain why bail had been granted for an espionage charge, regarded as one of the gravest offenses. Nonetheless, it seemed clear that he was referring to Mr. Esfahani.
Western analysts following the progression of the nuclear agreement said the arrest was worrisome.
Cliff Kupchan, the chairman of the Eurasia Group, a political risk consultancy in Washington, said in an email that it was a clear sign that Iran’s supreme leader, Ayatollah Ali Khamenei, “is unhappy over the slow pace at which the deal has been implemented.”
There was no immediate comment on Mr. Esfahani’s fate from the government of Canada, which has been contending with the arrest of another dual citizen in Iran in recent weeks.
In July, the Iranian authorities arrested Homa Hoodfar, a Canadian-Iranian anthropologist who studies the role of women in Muslim societies. The reason for her incarceration has not been made clear.
The nuclear-related arrest was one of a number of hostile signals from Iran recently.
Three weeks ago, the authorities announced the execution of a nuclear scientist who had returned home from the United States, where, he claimed, he had been kidnapped by the C.I.A. The Iranians said the scientist had betrayed secrets to the enemy.
And last week, high-speed boats from Iran’s Islamic Revolutionary Guard Corps Navy harassed American warships patrolling international waters in the Persian Gulf region at least four times, United States officials said, calling the actions dangerous and illegal.
Ayatollah Khamenei, who supported the nuclear agreement, has increasingly denounced what he calls American duplicity in the negotiation and other matters.
In a speech on Sunday reported by the state news media, for example, he criticized the United States for opposing Iran’s purchase of a Russian-made missile-defense system.
“We face such an enemy that does not recognize any right of defense for our nation,” the state news media reported Ayatollah Khamenei saying in the speech to air force commanders. “In fact, it says you should remain defenseless so that when we wish, we can invade you.”