Ciudad Juarez, Mexico: Hundreds of people blocked bridges to the US in three border cities on Tuesday, demanding the army leave in another challenge for the Mexican government as it struggles to quell escalating drug violence.

The protests in Ciudad Juarez blocked traffic for about two hours across three bridges connecting the city to El Paso, Texas. Similar protests broke out on bridges in the border cities of Nuevo Laredo and Reynosa. Demonstrators blocked city hall and a main avenue in the northern industrial city of Monterrey and roads in the Gulf state of Veracruz.

It was the largest display of discontent against the army's role in an anti-drug crackdown since President Felipe Calderon began deploying soldiers across the country two years ago to fight cartels. About 45,000 soldiers are now spread out across Mexico.

Government and army officials claimed that drug cartels organised similar protests in Monterrey earlier this month to undermine the crackdown. Federal officials had no immediate comment on Tuesday's protests.

Human rights activists say there are legitimate complaints about abuses by soldiers, including cases in which patrols allegedly opened fire on civilians. But they say it is unclear who has been behind the demonstrations. Calderon's offensive was initially popular among Mexicans hopeful for an end to violence.