The Queen has expressed "deep sympathy" for the families and friends of people killed in the storms that have hit Alabama and the southern United States.
In a message to US president Barack Obama, released by Buckingham Palace, the Queen said: "I have been appalled and saddened to hear of the tragic loss of life caused by the terrible storms that have hit Alabama and the south of the United States.
"Please pass on my deep sympathy to the families and friends of all those who have been killed and to all those who have been affected."
The Queen's message comes after the storms last week flattened homes in a stretch of land from Mississippi to Virginia.
At least 342 people were killed, including 250 in Alabama, and thousands more were hurt. There were also 35 deaths in Mississippi, 34 in Tennessee, 15 in Georgia, five in Virginia, two in Louisiana and one in Kentucky.
The Red Cross opened emergency shelters as the authorities were faced with the task of finding more permanent housing for the thousands without homes.
In Alabama, 2,000 National Guard troops were dispatched to help residents and keep the peace. Many blocked off roads or patrolled neighbourhoods to keep away spectators and looters.
Homeland security secretary Janet Napolitano led a delegation of senior US government officials to tour hard-hit areas in Alabama and Mississippi to pledge support for residents.
President Obama, who visited Alabama on Friday, has already signed disaster declarations for those two states and Georgia.