In a new sign that drug-gang violence targeting Mexican law enforcement is bleeding across the border, Mexican drug gangs (search) are now offering a bounty for killing U.S. border agents and state and local law enforcers.

U.S. intelligence shows that Mexico's violent and notorious drug-trafficking gang, The Zetas (search), is targeting the officers, offering $30,000 to $50,000 per assassination.

"That is a concern for a lot of us, you know, because these guys are trying to get their product across and we're the blockade here," said Bill Jenkins Jr., assistant chief patrol agent with U.S. Customs and Border Protection, which is part of the Homeland Security Department (search).

The agency confiscated nearly 15,000 pounds of cocaine and more than 1 million pounds of marijuana (search) last year — just a dent in the multibillion-dollar narcotics trade that, especially on the Mexican side of the border, is increasingly violent between the drug gangs and Mexican law enforcement. In the past couple of weeks, drug gangs are suspected of killing two Mexican cops in Nuevo Laredo and killing three federal agents in a massacre of nine people near Cancun.

"That's their economy and we're the stumbling block there. If we're taking away from the profits, they might be getting desperate," Jenkins said.

And with $50,000 bounties, they're getting more ruthless.

Click in the box near the top of the story to watch a report by FOX News' Phil Keating.