Regulators probing

American International Group

(AIG) - Get Report

have trained their sights on

Munich Re

, the giant German company that has done copious business with America's biggest insurer, a person familiar with the investigation says.

In another development, Maurice Greenberg, AIG's former longtime chieftain, and two other former AIG executives resigned from the board of

Transatlantic

(TRH)

, a reinsurance firm that is a majority-owned AIG subsidiary.

State and federal regulators are expected to meet today with Munich Re executives to discuss whether the reinsurer made any "misrepresentations" about some of its business deals with AIG, the person said.

Articles on

TheStreet.com

last week chronicled

Munich Re's close ties to AIG and disclosed that the company

owns a 49% equity investment in Richmond Insurance, the Bermuda-based reinsurer that served as a dumping ground for the big firm's unwanted policies.

Munich Re spokeswoman Anke Rosumek says regulators requested the meeting as part of the process of "gathering information" for their investigation.

"In this connection Munich Re has now been asked to provide information and (as in other cases before) we are fully cooperating with the authorities," Rosumek wrote in reply to questions.

The meeting with Munich Re was first reported by CNBC. An AIG spokesman said he was not aware of the meeting.

For more than a decade, AIG, citing its minority 19% equity interest in Richmond, had treated Richmond as an independent business that needn't be included in AIG's financial statements. Last week, AIG said it recently discovered "previously undisclosed evidence" of its control of Richmond. In light of that, AIG will begin treating Richmond as a subsidiary, something it may be forced to do with at least two other little-known offshore reinsurers.

Several former AIG employees -- all of whom were interviewed previously by

TheStreet.com

on condition of anonymity -- believe Munich Re got involved in Richmond as a favor to one of its major customers. AIG has had a longstanding business relationship with the German-based reinsurer.

As for Transatlantic, the AIG subsidiary announced late Monday that Greenberg, Edward Matthews and Howard Smith have resigned from the company's nine-member board. Greenberg, who was forced to step down as AIG's chairman and chief executive office after nearly 40 years in those posts because of the investigation, had been Transatlantic's chairman.

Smith, AIG's former CFO, was fired March 22 for refusing to cooperate with the joint state and federal investigation. AIG's board ousted its finance officer after learning that Smith had asserted his constitutional right against self-incrimination during an interview with investigators.

Transatlantic announced the resignations a day after

TheStreet.com

reported that the former AIG executives remained on the company's board.

A person close to the investigation says regulators are looking into some of the business dealings between the two companies.

AIG, which spun off Transatlantic in 1990, owns 60% of the company's stock. AIG is a significant business partner of Transatlantic, representing about 15% of its reinsurance premium revenue.