TOKYO— Tokyo Electric Power Co. said Friday that 26 U.S. residents are suing the company over claims that they were exposed to radiation while on a rescue mission as crew members of a U.S. naval carrier following the March 2011 earthquake, tsunami and nuclear crisis that devastated northern Japan.

A group of sailors who served on the aircraft carrier Ronald Reagan during the rescue mission to Japan filed the suit in December in U.S. District Court in San Diego. In the complaint, the crew members accused Tepco of negligence after the disaster and alleged that company officials knew more about the potential health risks of the nuclear crisis at the Fukushima Daiichi nuclear complex than they told U.S. officials who were coordinating assistance.

Since December, more Ronald Reagan crew members have joined the suit as plaintiffs, said Paul Garner, a California attorney who is representing the plaintiffs in the case.

"We're in the process of adding new plaintiffs to this lawsuit," Mr. Garner said Friday in an interview. "The facts have to come out."

The plaintiffs are asking for Tepco to set aside at least $1 billion for a fund to cover the crew members' medical treatment and health costs related to illnesses following their alleged exposure to radiation in Japan.