Citing unnamed diplomats and law enforcement officials, the newspaper yesterday said the effort includes more information-sharing and training than previously known.
A wave of suspected drug-related violence has left more than 28,000 dead across Mexico since 2006, according to official figures.More than 2,700 people have been killed this year alone in Ciudad Juarez, a city of some 1.3 million.
More than 50 killings in the border city in the past two years were of US citizens.
The US assistance has enabled the Mexican marines to carry out the kind of rapid-strike operations undertaken by US forces against Taliban leaders in Afghanistan, the report said.
Based in the US embassy in Mexico City and in consulates along the US-Mexican border, for example in Matamoros, agents of the Drug Enforcement Administration deliver "intelligence packages" about the location of drug bosses to the Mexican marines, The Post said.
The marines then go into action, sometimes capturing, sometimes killing their targets in spectacular urban firefights often within hours, the paper noted.Mexican officials deny that the US military is training Mexican marines, and the Pentagon declines to discuss the training, The Post said.
But US officials and recently leaked diplomatic cables confirm that the US military is conducting urban-combat and counterinsurgency instruction in Mexico and the US, the report pointed out.