Eight out of the 12 top US gun dealers whose products fuel Mexico's drug violence are located in the state of Texas, The Washington Post reported.

The newspaper said it had uncovered the names of 12 top US dealers of guns traced to Mexico in the past two years following a year-long investigation.

More than 28,000 people have died across Mexico since 2006, when the government launched a massive military operation to root out drug traffickers and organized crime.

The identities of US dealers who had sold guns seized at Mexican crime scenes remain confidential under a law passed by Congress in 2003, the report said.

But The Post said it now knew that eight of the top 12 dealers were in Texas, three in Arizona, and one in California.

In Texas, two of the four Houston-area Carter's Country stores are on the list, along with four gun retailers in the Rio Grande Valley at the southern tip of the state, according to the report.

There are 3,800 gun retailers in Texas, 300 in Houston alone.

"One of the reasons that Houston is the number one source, you can go to a different gun store for a month and never hit the same gun store," the paper quoted Dewey Webb, a special agent in charge of the Houston field division of the Bureau of Alcohol, Tobacco, Firearms and Explosives, as saying.

"You can buy (a 9mm handgun) down along the border, but if you come to Houston, you can probably buy it cheaper because there's more dealers, there's more competition."