MEXICO CITY, Dec 12 (Reuters) - Mexican army troops have captured a top commander of the powerful Gulf Cartel drug mafia who ran the gang's division of hitmen, the government said on Wednesday.

Soldiers arrested Marco Ramirez del Rio, known as "Tony la Palma," together with two other suspected cartel members in the northern border state of Tamaulipas, a major shipment point in the traffic of cocaine from South America to the United States.

A fourth suspect committed suicide to avoid capture, the Attorney General's office said in a statement.

It was not clear if the men had resisted arrest, though the government said they were armed with several assault rifles and pistols.

President Felipe Calderon has sent 25,000 soldiers and police into smuggling hot spots in the past year, putting thousands of people linked to the drug trade behind bars.

The Gulf cartel, which relies on its armed wing, the Zetas, dominates smuggling routes into Texas via the Mexican border cities of Matamoros, Reynosa and Nuevo Laredo.

Ramirez de Rio narrowly escaped capture in June when authorities nabbed his boss, Luis Reyes, a former soldier who led the Zetas, the Attorney General's office said.

The government said Ramirez de Rio had taken over Reyes' job and ran trafficking in five states, including Tamaulipas.

The U.S. Embassy described Ramirez del Rio as the cartel's No. 3 man, though his name was not on a list of gang leaders distributed by Mexican police earlier in the year.

Despite Calderon's war on the traffickers, drug-related murders continue unabated and are set to top 2,500 this year, up from 2,100 in 2006, officials say.

Mexico is still awaiting a delivery date for $1.4 billion in drug-fighting equipment pledged by the United States, amid signs U.S. lawmakers may try to attach conditions to the aid. (Reporting by Jason Lange, editing by Todd Eastham)

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