MONTERREY, Mexico (Reuters) - Hundreds of Mexicans blocked roads and bridges into the United States on Tuesday in a protest of army operations against drug gangs that officials said was organized by drug traffickers.

About 300 protesters, some with handkerchiefs tied over their faces, carried signs saying “Army Get Out!” in front of the town hall in the northern city of Monterrey, 130 miles from the Texan border. It was the largest in a series of anti-army protests this week.

In a growing challenge to the military across Mexico, small groups of taxi drivers also blocked bridges that connect the border cities of Reynosa and Nuevo Laredo with Texas, stopping vehicles and foot passengers, police said.

Hundreds of miles away, another 300 people shut highways in the Gulf city of Veracruz to pressure the military to go back to their bases.

The demonstrations put fresh pressure on President Felipe Calderon to defeat the cartels after two years of an army-backed campaign and spiraling drug violence.

Calderon said on Monday the rampant violence that killed 6,000 people last year shows drug cartels are desperate, but drug trade experts say Mexico’s deepening economic slump and rising joblessness could attract more recruits to the trade.

Natividad Gonzalez, governor of Nuevo Leon state, blamed Mexico’s most violent drug gang, the Gulf cartel, and its armed wing The Zetas for the protests.

“There are reasons to believe it has to do with the Gulf cartel and the group known as The Zetas,” he told a news conference.

State police chief Aldo Fasci said last week that crime organizations were paying people to protest against the army and that gangs were handing out backpacks full of school books, pens and paper to poor families who joined the demonstrations.

The northern states of Nuevo Leon and Tamaulipas, home to Monterrey, Nuevo Laredo and Reynosa, are the main trafficking routes into Texas for the powerful Gulf Cartel and its feared armed wing, the Zetas, who behead their enemies.

One woman at the protest who declined to be named told Reuters she came with a neighbor who had been paid to turn up.

Mexico’s drug war has scared off investors and worried the United States, which is giving $1.4 billion worth of equipment and other aid to help Mexico and Central America fight cartels.

GUN BATTLE

At least five people died in a gun battle between troops and drug hitmen in Reynosa on Tuesday, police said, but added that the violence was not related to the protests.

Calderon has sent 45,000 troops and federal police across Mexico to fight drug gangs since late 2006, a move widely supported by Mexicans angry with years of inaction and the deep corruption in the country’s police forces.

Despite warnings from rights groups about soldiers using excessive force in the drug fight, Calderon also has Washington’s support for the army, which has made historic drug seizures and is catching more gang leaders.

“Rising levels of unemployment in Mexico make it much easier for Mexican drug traffickers to recruit youths to engage in demonstrations like this, for relatively low pay,” U.S.-based security consultancy Stratfor said in a report.