captured Mexican crime boss said his gang purchased weapons in the United States and smuggled them across the Rio Grande river,

according to testimony released Tuesday by Mexican authorities.

Jesus Enrique Rejon Aguilar, one of the founders and leaders of the feared Zetas drug cartel, said smugglers began transporting the weapons across the river following increased security at international crossings.

"All the arms are bought in the United States... Before we would transport them over the bridges, but now we transport them across the river, with difficulty," he said, according to the public security ministry.

The Rio Grande -- known as the Rio Bravo del Norte in Mexico -- forms the 1,200-mile (2,000 kilometer) border between Mexico and the US state of Texas.

Mexico has long called for stricter gun laws in the United States, which is believed to be the source of much of the weapons that end up in the hands of drug traffickers and is also one of their most lucrative markets.

Some 37,000 people have been killed in mostly drug-related violence in Mexico since 2006, when the government launched a massive military crackdown on the powerful cartels, which also battle each other over territory.

Rejon Aguilar was detained on Sunday in central Mexico as he was traveling to the south of the country to visit his mother in his home state of Campeche, according to Mexican authorities.

He was one of the founders of the Zetas cartel, a group of former soldiers who pioneered the use of military tactics and weaponry, at first in the service of the Gulf cartel, for which they worked as hitmen.

They later split from their employers and founded their own cartel, sparking a brutal turf war. The Zetas are accused of two mass killings, one in Mexico's northeast and one in a Guatemalan border province.