More than a quarter of the all-cash luxury home purchases made using shell companies in Manhattan and Miami were flagged as suspicious in a new effort to unearth money laundering in real estate, the Treasury Department said Wednesday. As a result, officials said they would expand the program to other areas across the country.

The expansion of the effort to identify and track the people behind shell companies, begun in March, means that there will now be increased scrutiny of luxury real estate purchases made in cash in all five boroughs of New York City, counties north of Miami, Los Angeles County, San Diego County, the three counties around San Francisco and the county that includes San Antonio.

The examination, known as a geographic targeting order, is part of a broad effort by the federal government to crack down on money laundering and secretive shell companies.

"The information we have obtained from our initial G.T.O.s suggests that we are on the right track," Jamal El-Hindi, the acting director of the Financial Crimes Enforcement Network within the Treasury, said in a department news release. "By expanding the G.T.O.s to other major cities, we will learn even more about the money laundering risks in the national real estate markets, helping us determine our future regulatory course."

Among the suspicious transactions that the Treasury Department found tied to sales in New York or Miami this year were a $16 million cash withdrawal, a person involved in counterfeit checks and someone involved in moving $7 million around in shell companies associated with South America, Treasury officials said.

The areas being added to the order are places where buyers frequently purchase luxury real estate using shell companies, the officials said. The dollar values involved purchases of more than $500,000 or more in Bexar County, which includes San Antonio; $1 million in Florida; $2 million in California; $3 million in Manhattan; and $1.5 million in the other boroughs of New York City. Title insurance companies, which are involved in virtually all real estate transactions, are charged with carrying out the order.