St. Louis ? An ice storm slickened roads and sidewalks, grounded hundreds of flights, and cut power to tens of thousands Sunday in a swath from the Southern Plains to the Great Lakes as even colder weather threatened.

The wintry weather was expected to continue through midweek, and ice storm warnings stretched from Texas to Pennsylvania.

Six traffic deaths were blamed on icy roads in Oklahoma. Roads along much of the state were considered slick and hazardous by the Oklahoma Department of Transportation, with two sections of Interstate 40 being closed temporarily.

More than 130,000 customers lost power in Missouri, Oklahoma, Illinois and Kansas, utilities reported.

Some communities in Missouri reported ice as thick as three-quarters of an inch, the National Weather Service said.

Missouri Gov. Matt Blunt declared a state of emergency and activated the National Guard.

Chicago’s O’Hare International Airport, one of the nation’s busiest, canceled more than 400 flights. The airports in Kansas City, Mo., and St. Louis also canceled several flights.