New York ? The tornadoes that ravaged portions of the Midwest and the South in early May could be the costliest ever for U.S. insurers, an insurance group said Monday.

Actual claims filed now exceed $1 billion, and damage assessments continue in the affected communities, according to the Insurance Information Institute, a trade group.

“While the industry has the capacity to pay these claims, these latest storms substantiate what the industry has been seeing for years,” said Robert Hartwig, Insurance Information Institute’s chief economist, in a statement.

“Homeowners insurance rates in many parts of the country continue to rise because of the extraordinary costs associated with paying these claims,” he said.

More than 40 people were killed and there were more than 400 reports of tornadoes between May 2 and May 11.

Last week, AIR Worldwide, a Boston weather and catastrophe risk modeling firm, said insured losses from the storm could exceed $2.2 billion.

According to Insurance Information Institute, the costliest tornado event was an April 2001 storm that spawned hail, severe wind and tornadoes in 16 states over a seven-day period. That event cost insurers $1.93 billion.

Insurance Services Office Inc., a Jersey City, N.J., company that tracks claims data, has classified the May storms as a catastrophe in 18 states. The states are Oklahoma, South Dakota, Kansas, Missouri, Alabama, Arkansas, Georgia, Mississippi, North Carolina, South Carolina, Tennessee, Iowa, Florida, Kentucky, Nebraska, Colorado, Indiana and Ohio.

Insurance Services Office Inc. expects to issue a preliminary claims estimate later this week.

Even before the tornadoes, spring was shaping up to be a costly period for insurers. A storm in early April cost the industry $1.2 billion.