CAIRO, Egypt — Iran has detained an Iranian-American consultant working for George Soros’s Open Society Institute, the latest American citizen connected to a nongovernmental organization to be seized in the country, the institute said yesterday.

The detention of Kian Tajbakhsh comes amid recent accusations by Iranian authorities that America is using critics and dissidents to try to overthrow the country’s hardline government.

Earlier this month, Iranian authorities arrested the director of the Middle East Program at the Washington-based Woodrow Wilson Center for Scholars, Haleh Esfandiari, and charged her with setting up a network to overthrow the Islamic regime.

Mr. Tajbakhsh, an urban planning consultant who has also worked for the World Bank, was detained on or around May 11, the New York-based Open Society Institute said in a statement. The group is a private foundation that encourages democracy building in countries around the world.

“We are concerned for his safety and call for his immediate release,” the statement said.

The institute said the 45-year-old Mr. Tajbakhsh had been consulting “to facilitate public health, humanitarian assistance and urban planning projects that we undertook openly and with the knowledge of the Iranian government.”

Mr. Tajbakhsh, who has been a consultant with the group since 2004, is also a senior research fellow at the New School in New York, the statement said.

Another Iranian-American, journalist Parnaz Azima, who works for the American-funded Radio Farda, has been prohibited from leaving Iran since her passport was seized in January. She has been interrogated several times by intelligence agents, the press watchdog group Reporters Without Borders said in a statement yesterday.

Another American, former FBI agent Robert Levinson, disappeared in March after going to Iran’s resort island of Kish, and his whereabouts are unknown.