LAS VEGAS (AP) — Anthem Blue Cross Blue Shield will leave Nevada's health care exchange next year, an abrupt move that will force about a fourth of the state's current exchange enrollees to look for another carrier.

State officials on Monday decried the insurer's decision to pull its plans from three of Nevada's more populous counties. The move from the Indianapolis-based carrier came only weeks after it said it would not offer plans through the government-run but privately administered health insurance exchange in the state's other 14 counties.

"I am frustrated and disappointed with Anthem's surprise and abrupt decision to leave the healthcare exchange especially during uncertain times," Nevada Gov. Brian Sandoval said in a statement. "This is a significant blow to the state's individual marketplace ..."

More than 89,000 people are covered through the Silver State Exchange, which was created as part of former President Barack Obama's landmark health care law. It is meant to be used by people who do not get insurance through their employer or another government program. Of that number, 22,000 people have a plan with Anthem.

The insurer in a statement attributed its decision to market volatility, explaining that planning and pricing for plans that are compliant with the Affordable Care Act have "become increasingly difficult" for reasons including changes and uncertainty surrounding federal operations and regulations, such as the subsidies for enrollees.

Nevada is not the only state looking at insurers leaving exchanges. Missouri, Ohio and Washington state also have several largely rural counties where no insurance company will participate in the marketplace in 2018.

Two insurers, SilverSummit Healthplan and Health Plan of Nevada, will offer plans in 2018 on the exchange in Clark, Washoe and Nye counties. SilverSummit Healthplan will make its debut, while Health Plan of Nevada is proposing average rate increases of 26.1 percent.

Janel Davis, the communications director for the exchange, said those affected by the insurer's move will receive a letter notifying them of the change. She said the agency will transition the consumers in Clark, Washoe and Nye counties to "a similarly priced plan," but individuals are strongly encouraged to shop for coverage on the marketplace.

This year's open enrollment will run from Nov. 1 through Dec. 15. State officials are "currently having conversations" with carriers in an effort to have an on-exchange option available to residents of Nevada's 14 mostly rural counties, Davis said.

"The exchange remains committed to assisting consumers," she said.