MEXICO CITY – A day after marines killed a reputed powerful drug lord, dozens of ominous banners apparently hung by rivals appeared Saturday in cities across Mexico's Gulf coast with messages gloating about his demise.

The signs, hung on pedestrian bridges and other public places but quickly taken down by authorities, reinforced fears that the death of alleged Gulf cartel leader Antonio Ezequiel Cardenas Guillen will further empower the Zetas, a gang of hit men formed more than a decade ago by renegade Mexican soldiers that has become one of Mexico's most brutal and feared drug gangs.

Former allies of the Gulf cartel, the Zetas went independent earlier this year, unleashing a turf battle along the northeastern border with the United States that has at times reached the level of all-out war.

Drug gangs used vehicles to put up roadblocks Saturday morning in Reynosa, a city across from McAllen, Texas, according to Twitter messages from the Reynosa city government warning citizens to travel with caution. It was unclear if the roadblocks were related to the death of Cardenas Guillen.

Such blockades have become a near-daily gang tactic in northeastern Mexico.

But Friday night, buses and cars were used to block roads and highways in the western city of Morelia — stronghold of La Familia cartel — suggesting that the tactic could be spreading across Mexico. Several vehicles were torched, and one driver was injured when assailants stole his bus to use in the blockades, according to the attorney general's office of Michoacan state.

Cardenas Guillen, known as "Tony Tormenta" or "Tony the Storm," was killed Friday during a two-hour shootout in an operation that included 150 marines, three helicopters and 17 military vehicles, the Mexican navy said in a statement. Four of his gunmen and three marines also died during the fighting in the city of Matamoros, across from Brownsville, Texas. A local reporter and a soldier were killed in related mayhem.

President Barack Obama called his Mexican counterpart, Felipe Calderon, on Saturday morning to reaffirm U.S. support for Mexico's efforts to fight the cartels, and express his condolences for the troops killed in the shootouts, according to a White House statement.

Mexican presidential security spokesman Alejandro Poire touted Cardenas Guillen's downfall as "another meaningful step toward the dismantling of criminal groups."

The Zetas, apparently, also celebrated.

The banners, which appeared in several cities of northeastern Tamaulipas state, neighboring Veracruz state, and in the resort city of Cancun on the Yucatan Peninsula, crowed: "Once again the destiny of the traitors has been demonstrated, crushing the Gulf traitors."

They were signed, "Sincerely, the Zetas Unit."