The US government has approved the potential sale of 18 UH-60M Black Hawk helicopters - built by Sikorsky Aircraft, a unit of United Technologies Corp - to Mexico, a deal valued at $680 million.

The State Department has already approved the possible sale and Congress was notified last Thursday by the Pentagon's Defense Security Cooperation Agency, which oversees foreign arms sales.

US lawmakers have 30 days to block the sale, although such action is rare.

The deal was announced ahead of the upcoming trip to Mexico by Defense Secretary Chuck Hagel.

Mexico had asked to buy 18 UH-60M Black Hawk helicopters, 40 engines built by General Electric, night vision goggles, weapons, and other equipment, as well as training and logistics support.

The Defense Security Cooperation Agency said the sale would significantly increase and strengthen Mexico's ability to provide in-country airlift support for forces fighting drug trafficking organizations.