(Reuters) - Authorities in Eagle Pass, Texas, have reopened one of the city's two border crossings to Mexico which had been closed for several hours due to safety concerns, the U.S. Customs and Border Protection agency said.

The agency said local authorities reopened Bridge II, which handles commercial traffic to and from the city of Piedras Negras, Mexico, at 4:20 p.m. local time.

The commercial crossing was shut down nearly six hours earlier over safety concerns which local news media said were prompted by the discovery of a "suspicious device."

Eagle Pass is not one of the principal hubs for trade or visitors over the nearly 2,000-mile (3,200-km) U.S. Mexico border.

The agency said that while the temporary closure "caused an interruption in the trade process," a special agreement with Mexican authorities allowed for trucks to be processed "after normal business hours."

Operations and traffic across Bridge I continued to flow as normal throughout the day.

News reports on local KSAT.com identified the threat as a "suspicious device", possibly a grenade, although the border protection agency declined to comment.

(Reporting By Tim Gaynor; editing by Mohammad Zargham and Cynthia Osterman)