MEXICO CITY (Reuters) - Gunfights broke out and vehicles were set ablaze on Friday in one of Mexico's biggest cities along the U.S. border, after security forces arrested a leader of one of the main drug gangs in the area.

Activity in parts of Reynosa, a city across the Rio Grande from McAllen, Texas, ground to a halt on Friday afternoon after vehicles were torched and shooting began, authorities said.

Earlier in the day, federal police and marines captured "El Gafe," a leader of the Gulf Cartel, said a spokesman for police in Reynosa, a city of more than 600,000 people in the northeastern state of Tamaulipas.

A federal government security official, speaking on condition of anonymity, identified "El Gafe" as Jose Hugo Rodriguez Sanchez.

The official had earlier named the cartel boss as Jose Tiburcio Hernandez Fuentes. Later, he clarified that Hernandez was a different suspected gang member also captured.

Three suspected assailants were killed, and two state police were injured, the Tamaulipas state government said in a statement. The Reynosa police spokesman said two bystanders were apparently killed, but this was not confirmed.

El Gafe was taken to Mexico City, he added.

Reynosa has been one of the most violent cities in Mexico over the past year, racked by turf wars among the Gulf Cartel and the Zetas, two drug gangs fighting for control of border smuggling routes and crime rackets.

"The city is completely out of control," said Francisco Garcia Cabeza de Vaca, an opposition senator and former mayor of Reynosa.

More than 100,000 people have died in gang-related violence in Mexico over the past eight years. President Enrique Pena Nieto pledged to restore order when he took office in 2012, but although the homicide count has fallen, parts of the country remain mired in violence.

(Reporting by Dave Graham and Anahi Rama; Editing by Lisa Shumaker and Ken Wills)