A grand jury issued a subpoena to oil field services company Halliburton Co. (search) seeking information about its Cayman Islands (search) unit's work in Iran, where it is illegal for U.S. companies to operate, Halliburton said on Monday.

The company, formerly headed by Vice President Dick Cheney (search), said it understood the investigation of its subsidiary's work in Iran had been transferred to the U.S. Department of Justice from the Treasury Department, which first initiated an inquiry in 2001.

"In July 2004, Halliburton received from an Assistant U.S. Attorney for the Southern District of Texas a grand jury subpoena requesting the production of documents. We intend to cooperate with the government's investigation," Halliburton said in a filing to the U.S. Securities and Exchange Commission.

Halliburton said it had previously replied to requests for information from the Treasury Department's Office of Foreign Assets Control in 2001 and again in January 2004.

Halliburton's engineering and construction unit KBR, formerly called Kellogg Brown & Root, is also the subject of U.S. Justice Department and SEC investigations for possible overcharges for fuel and food service contracts in Iraq, where it is the largest contractor.

Halliburton said it would comply with the subpoena, and reiterated it believed its links to Iran through the Cayman Islands unit were in compliance with applicable laws and regulations.

The company said in its annual report that revenues from its subsidiary's business in Iran amounted to about half of 1 percent of total revenues of $16.3 billion in 2003, or about $80 million.

"It is important to understand, especially in the current political environment, that this is not a condemnation of the company, but a method of further studying the facts. We welcome a thorough review of any and all of the company's business," Halliburton spokeswoman Wendy Hall said in an e-mail.

In a report issued in October 2003 in response to shareholder complaints about its Iranian links, Halliburton said it was not illegal for U.S. companies' independent foreign subsidiaries to conduct business in Iran, and that it had taken steps to isolate its U.S. operations and managers from its work there.