By Carey Gillam

KANSAS CITY, Mo., Dec 10 (Reuters) - A deadly ice storm sweeping through the U.S. Plains left about 400,000 people without power as temperatures plunged and was blamed for at least 12 deaths, authorities said on Monday.

The icy blast downed tree limbs and power lines, leaving more than 311,000 people without power in Oklahoma and shutting down electricity service to more than 80,000 people in Missouri, more than 10,000 people in Illinois and more than 4,000 in Kansas.

Conditions were expected to only worsen Monday afternoon, according to the National Weather Service, which predicted the potential for damaging ice accumulations as a cold air mass stalls over the region.

Ice storm warnings were issued from Texas up through Oklahoma and Kansas and east across Missouri into Illinois, with up to an inch of ice accumulation possible in some areas. Iowa and Arkansas were also affected.

"We expect a lot more, especially with another round of freezing precipitation that will be making its way through this afternoon," said Oklahoma Department of Emergency Management spokeswoman Michelann Ooten. "We are getting ready to deploy some generators to some communities that requested them, and we may be calling on the National Guard for transport."

Missouri Gov. Matt Blunt declared a state of emergency Sunday, calling out the state's National Guard to aid communities hit by the storm.

Ice-slicked roads contributed to the deaths of 11 people in Oklahoma over the weekend, including four who died in a pile-up that involved a tractor-trailer, state officials said. One Oklahoma man died of hypothermia.

No deaths were reported in Missouri but a Lamar, Missouri, man was injured when a ice-covered tree fell on him.

Parts of Interstate 70 were closed and hundreds of flights were canceled at the major airports in Chicago, Kansas City, St. Louis and Oklahoma City.

The National Weather Service office in Norman, Oklahoma, reported ice accumulations on trees and power lines from a quarter to an inch thick in areas of central Oklahoma.

Ty Judd, a weather service meteorologist, said the freezing rain could continue into Tuesday, although the state could get a reprieve.

"We might see the temperatures go over the freezing mark this afternoon, which would help the situation," Judd said. (Reporting by Ben Fenwick in Oklahoma City and Carey Gillam in Kansas City, editing by Doina Chiacu)

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