U.S. lawmakers on both sides of the aisle are weighing actions to allow U.S. agents working in Mexico to pack heat after a drug gang killed an unarmed U.S. immigration agent and wounded another.

U.S. agents have not been allowed to carry weapons in Mexico since a 1990 agreement. But their safety has been increasingly in jeopardy ever since Mexican President Felipe Calederon declared war on the drug cartels when he took office in December 2006.

"It is essential that the U.S. government conduct a comprehensive threat assessment to protect U.S. government personnel working in Mexico," said Rep. Peter King, R-N.Y., the chairman of the House Homeland Security Committee. "We must also talk to the Mexicans about their prohibition against U.S. personnel carrying weapons and determine the extent to which security details must be expanded."

A Homeland subcommittee led by Rep. Mike McCaul, R-Texas, is planning a hearing next month to probe the U.S. role in Mexico's war on its drug cartels.

"The Mexican government doesn't allow our law enforcement to carry weapons in Mexico. It seems to me we're assisting them in this war against the drug cartels. Our law enforcement should be armed," McCaul told Fox News. "These two agents were sitting ducks and sitting targets in what was an intentional ambush.

Immigrations and Customs Agents Jaime Zapata and Victor Avila were shot on a federal highway while traveling in the northern state of San Luis Potosi en route to Mexico City on Feb. 15. The area is at the center of a power struggle between two rival drug gangs, the Zetas and the Gulf Cartel. Zapata was killed, the first murder of a U.S. agent in the line of duty of Mexico's drug war.

The Mexican Defense Department said Wednesday that a suspect was detained but provided little additional information.

U.S. Homeland Security Secretary Janet Napolitano and U.S. Attorney General Eric Holder attended Zapata's funeral Tuesday in his hometown of Brownsville, Texas. Both vowed to continue helping Mexico in its war against drug cartels battling for lucrative trafficking routes into the United States.

The Homeland Security and Justice Departments formed a joint task force led by the FBI to help Mexico find the killers.

Rep. Sheila Jackson Lee, D-Texas, told FoxNews.com that she introduced bipartisan legislation in the last session of Congress and on the first day of the current session to give additional tools to DEA, ATF, CPB agents on the U.S. border so that they are prepared with the weapons to confront the violence.

"Officers cannot enforce laws without good equipment," she said.

McCaul said the attack was a "game changer" because the operating assumption for more than 25 years was that drug cartels would not target or kill a U.S. agent.

"I see this assault as a direct assault on the United States and I think the United States needs to respond accordingly," he said.