April 28, 2014 - 11:35 AMT
PanARMENIAN.Net - Eleven of the victims were in several suburbs of Little Rock in Arkansas, a state official said, according to BBC News.
One other person was killed in the town of Quapaw in the north-east of Oklahoma where officials said many buildings were badly damaged.
Tornadoes also struck in Nebraska, Kansas, Iowa and Missouri.
Matt DeCample, a spokesman for Arkansas Governor Mike Beebe, said eleven people had been killed in several suburbs west and north of Little Rock - five in Faulkner County, five in Pulaski County and one in White County.
Congressman Tim Griffin told Reuters that an "entire neighborhood of 50 homes or so" in Faulkner County had been destroyed, with many "completely gone except the foundation".
First reports from Oklahoma said two people had died in Quapaw but officials later revised the figure down to one. Another six people were injured.
Quapaw, which has a population of about 900, was badly hit by the tornado, Ottawa County Emergency Management director Joe Dan Morgan said.
"Looks like about half of town got extensive damage as well as the fire department," he said.
The tornado then headed northwards into the state of Kansas where it struck Baxter Springs, injuring several people and causing further damage.
The Arkansas tornado touched down about 10 miles (16km) west of the city of Little Rock and left a 40 mile (65km) path of destruction.
It is said to have passed through several northern suburbs - including the town of Mayflower where it destroyed several buildings.
A witness in Mayflower reported a tornado half a mile wide crossing Interstate 40 on Sunday, April 27 evening, the National Weather Service said.
Over the weekend, storms struck the eastern part of the U.S., killing a child in North Carolina.