Mexico City ? An attacker threw an explosive device over the wall around the U.S. consulate in the border city of Nuevo Laredo, breaking windows and startling employees inside but causing no injuries, the U.S. Embassy said Saturday.

The attack, which took place Friday night, is under investigation, embassy spokesman Claude Young said.

Young said the consulate and the consular agency in the border town of Piedras Negras would be closed Monday pending a review of security measures.

Mexican federal prosecutors in the capital said they were reviewing evidence from the scene, including video feeds from security cameras at the consulate.

Nuevo Laredo, across the Rio Grande River from Laredo, Texas, and other cities have seen increased violence in recent weeks as powerful Mexican drug cartels battle over control of lucrative trafficking along the border.