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.