LITTLE ROCK, Ark. -- Wal-Mart Stores Inc. said Friday it will review all of its workers and fire any who are illegally employed, following a federal immigration sweep that resulted in the arrests of 245 employees.

Investigators told The Associated Press on the condition of anonymity that they gathered recordings from wiretaps that indicate Wal-Mart executives knew the company's subcontractors used illegal workers.

None of those arrests took place at Missouri stores.

Though contract cleaning crews were the focus of Thursday's sweep, a Wal-Mart spokeswoman said Friday that Wal-Mart employees at stores in Arizona and Kentucky were among those arrested.

"Approximately 10 Wal-Mart associates were arrested during the raids yesterday," said the spokeswoman, Mona Williams. "These are people who used to be part of the outside cleaning crew, and when we took that in-house, these folks were simply hired on as employees. They got caught up in the immigration sweep."

Wal-Mart, the world's largest retailer and the largest private employer in the United States, promised to cooperate with investigators. The company, which has 1.1 million domestic employees, has instructed store managers to preserve all relevant documents.

Agents left Wal-Mart's Bentonville headquarters with a number of boxes after searching the office of a midlevel executive.

Williams said Friday that no one at Wal-Mart had received a subpoena.

"We are doing a very thorough investigation with our own stores so we understand what happened and make sure that if we need to take pro-active, corrective steps, we will do that," she said.

"If we find workers that are undocumented we would terminate them immediately," Williams said.

The arrested workers came from 18 different nations, including 90 from Mexico, 35 from the Czech Republic, 22 from Mongolia and 20 from Brazil, said John Shewairy, a spokesman for Immigration and Customs Enforcement in Washington, D.C.

He would not reveal the names of companies that contracted with Wal-Mart. Williams also declined to release the names.

Maria Stephenson, an immigration lawyer in New Orleans, said a company hiring a subcontractor probably would not be held responsible if the subcontractor hired illegal aliens. She also said a company does not have to verify a prospective worker's documents.

"You don't have to call the (Department of Motor Vehicles) and verify that this person actually has a driver's license," she said.

Wal-Mart has been moving toward using its own workers to clean floors at its stores for about a year.

Initially, the government said it had arrested about 300 people. Shewairy said Friday that the number turned out to be 245.

Shewairy said the immigration agency does routine audits of companies throughout the country.

"When there is information that companies employ illegal aliens, we initiate our investigations," Shewairy said. An employer can face civil and criminal penalties for knowingly hiring illegal immigrants or failing to comply with certain employee recordkeeping regulations.