July was a record-breaking dry month in parts of the United States, with 12 percent of the country under an "exceptional" drought causing crop losses and water shortages, authorities said Monday.

The "exceptional" drought level, the highest on a five-step scale, spanned the largest amount of US territory since the National Drought Mitigation Center (NDMC) at the University of Nebraska began keeping records 12 years ago, it said.

"Exceptional drought's impacts include widespread crop and pasture losses, as well as shortages of water in reservoirs, streams and wells, creating water emergencies," the center said in a statement.

Close to 18 percent of the United States is experiencing exceptional or extreme drought, with much of it located in the southern United States, including South Carolina, Georgia, Florida, Louisiana and Texas.

The situation is getting worse, with the most recent weekly government drought report showing 41 percent of the United States facing some sort of abnormal dryness or drought, up from 36 percent the week prior.

Brian Fuchs, a climatologist at the NDMC, said moisture from Tropical Storm Don which has formed over the North Pacific Ocean and is expected to strengthen in the coming days, could bring some relief to parts of the US south.

"Whenever there is a lot of moisture in a short period of time, the potential exists for rapid improvement," Fuchs said.

"But while that possibility exists, it won't necessarily mean the end of drought in those areas. It will likely only improve by one drought category for those areas not impacted by any tropical storms."