NWG Natwest Group Plc

ZURICH—Zurich Insurance Group AG on Tuesday said it is considering a potential offer for the U.K. rival RSA Insurance Group PLC, a deal that could be valued at around $7 billion.

The Swiss insurer said it was responding to media speculation about a bid for its U.K. rival and that its announcement doesn't mean it will definitely make an offer for RSA. "There can be no assurance that any offer will be made," Zurich said.

London-listed RSA, which has a market capitalization of £ 4.45 billion ($6.9 billion), has been undergoing an overhaul since it appointed former Royal Bank of Scotland Group PLC Chief Executive Stephen Hester as its CEO.

Since joining RSA in early 2014 Mr. Hester has sold operations and raised fresh capital. Some of the changes stem from problems at its Irish unit that emerged in 2013.

Write to Neil MacLucas at neil.maclucas@wsj.com

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