Federal authorities moved in Wednesday to seize control of a New York City office building partially owned by a company with ties to the Iranian government.

The move by officials at the Treasury and Justice Departments is designed to stop the flow of funds they say are used to help Iran's efforts to build nuclear weapons.

The office tower, located on New York's famed Fifth Avenue, was built by an Iranian non-profit group in the 1970s. Over the years the ownership of the building has evolved into what federal officials say is an attempt to hide the stake held by an Iranian state-owned bank.

The government alleges that Assa Corp., the building's owner, is a shell company for Bank Melli, which is accused of facilitating the movement of nuclear materials for the Iranian government. Officials contend that Bank Melli was heavily involved in the day-to-day operations of Assa Corp. and its management of the Fifth Avenue building, which generated rental income that was sent back to Iran.

Although Treasury is now designating Bank Melli a front company for the Iranian government, it pointed out that the building houses legitimate tenants, including Merrill Lynch.

This designation does not interfere with the business and other activities of the tenants of 650 Fifth Avenue, Treasury said in a press release. People in the U.S. are not prohibited from dealing with business establishments or other tenants of the building.

An executive order signed by President Bush last year froze all Bank Melli assets in the United States. In October, the FBI seized a pair of Assa's bank accounts that held $3.1 million.

The sole employee of Assa, Mohammad Hassan Dhghani Tafti, engaged in a number of curious moves to apparently hide his employment status. His access to Assa accounts drew added attention from federal authorities. Between 2000 and 2007 more than $17 million was deposited into one of the seized accounts.

"This scheme to use a front company set up by Bank Melli -- a known proliferator -- to funnel money from the United States to Iran is yet another example of Iran's duplicity," said Stuart Levey, Treasury Undersecretary for Terrorism and Financial Intelligence.

Bank Melli is known to handle funds for the Iranian Revolutionary Guards Corps and its Qods Forces. Those groups are believed to help fund activities tied to the Taliban, Hizballah, Hamas and Palestinian Islamic Jihad.