(Reuters) - Singapore Telecommunications Ltd agreed to buy U.S.-based cyber-security firm Trustwave for $810 million, in a deal that will expand Southeast Asia's largest telecommunications operator's cloud-based services.

Trustwave will continue to operate as a stand-alone business unit, Singtel said.

"It will leverage Singtel Group Enterprise's assets and market presence to broaden its overall security portfolio and address the fast growing emerging security market opportunity in the Asia Pacific region," Singtel said in a statement.

Singtel will buy a 98 percent equity stake in the company, while Trustwave's chairman and chief executive officer, Robert McCullen, will hold 2 percent.