July was the hottest month in the contiguous United States since record-keeping began in 1895, government scientists have said, a trend that meteorologists attribute to climate change.

The searing July heat contributed to a widening of troubling drought conditions, now affecting 63 percent of the nation, the National Oceanic and Atmospheric Administration (NOAA) said Wednesday.

The average temperature in the contiguous United States -- excluding Hawaii and Alaska -- was 77.6 degrees Fahrenheit (25.3 Celsius), 3.3 degrees higher than the average for the entire 20th century, NOAA said.

The previous hottest July on record was July 1936, when the average temperature was 77.4 degrees.

The warm temperatures in July helped make the last 12 months the hottest on record in the United States, and contributed to a record-warm first seven months of the year, according to NOAA statistics.

The extreme heat and record dryness have created conditions ripe for wildfires, with more than two million acres (800,000 hectares) consumed in July, notably in Colorado.

California meanwhile had its fifth wettest July on record, and heavy rains were also seen in Nevada and along the western Gulf coast.

Kevin Trenberth, of the National Center for Atmospheric Research in Colorado, told AFP he was struck by how long the extreme heat had lasted.

"The fact that we are breaking records by so much and sustained for so long indicates that global warming is playing a role," Trenberth said.

He said the El Nino and La Nina climate patterns were also to blame.

A recent analysis of the past six decades of global temperatures by a group of scientists from the US space agency NASA showed a "stunning increase in the frequency of extremely hot summers," said one of the authors, James Hansen.

Hansen, who directs the NASA Goddard Institute for Space Studies, has said human-driven climate change is to blame for a series of increasingly hot summers and the situation is already worse than was expected two decades ago.

"My projections about increasing global temperature have been proved true. But I failed to fully explore how quickly that average rise would drive an increase in extreme weather," Hansen wrote in the Washington Post last week.

Hansen said the European heat wave of 2003, the Russian heat wave of 2010 and massive droughts in Texas and Oklahoma last year can each be attributed to climate change.