WASHINGTON — The southern United States in July endured the hottest single month ever recorded in any climate region nationwide, the National Oceanic and Atmospheric Administration said Monday.

The federal body's southern region -- Arkansas, Kansas, Louisiana, Mississippi, Oklahoma and Texas -- saw average temperatures of 86.1 degrees Fahrenheit (30 degrees Celsius) in July, NOAA said in a statement.

That topped the previous record average of 85.9 degrees Fahrenheit set in July 1980, it said.

July was the fourth warmest month ever nationwide, with average temperatures of 77 degrees Fahrenheit -- 2.7 degrees above the long-term average from 1901-2000.

Much of the United States has been sweltering in a steamy summer heatwave, with just seven states spared, all of them west of the Rocky Mountains, the only region where the average temperature was below the 20th century average.

In Texas, the city of Dallas got no relief, with temperatures above 100 degrees Fahrenheit on 30 out of 31 days in July.

The heatwave intensified drought conditions plaguing large swathes of the country, leaving the "largest exceptional drought footprint" in the US Drought Monitor's 12-year history, according to the NOAA.

July precipitation averaged just 2.46 inches (6.25 centimeters) nationwide -- 0.32 inches below the long-term average, it said.