The US Senate late on Thursday approved a 1.6-billion-dollar, three-year package of anti-drug assistance to Mexico, Central America and the Caribbean known as the "Merida Initiative."
The bill was approved by the House of Representatives on June 10, so the measure now goes to President George W. Bush to be signed into law.
Senate Majority Leader Harry Reid described the measure as "critical," and said its approval "shows the strong Congressional support on both sides of the aisle for working together to tackle shared problems with our neighbors on such a vexing issue."
"Mexico and the United States have a shared problem and we must have a shared solution," Reid said.
The senator said US officials "recognize that our voracious appetite for illegal narcotics has added to the problem at hand. We also recognize we must do more to stop the flow of the firearms contraband which is also exacerbating the problem."
The Merida Initiative was within the budget supplemental measure approved late on Thursday that included 162 billion dollars for the wars in Iraq and Afghanistan.
Congress cut 50 million dollars from the 450 million asked by Bush for Mexico for the first year of the initiative, and expanded by 65 million the sum for Central America, Haiti and the Dominican Republic.
The White House expressed its frustration with the reduced funding for Mexico.
"Well, it wasn't quite full funding that the president had asked for, so in that regard the president is not satisfied," White House spokeswoman Dana Perino said.
An underworld war between rival drug gangs and police has escalated into open bloody conflict in Mexico in recent weeks, with more than 1,500 people killed this year, some 500 of them in the northern border city of Ciudad Juarez alone.
On Thursday, unknown assailants shot to death a Federal Police commander and his bodyguard in a Mexico City restaurant in a brazen midday attack.
Gunmen on May 8 assassinated the acting federal police chief Edgar Millan. A day later assailants killed Esteban Robles, commander of Mexico City's anti-kidnapping police.
And top federal organized crime investigator Roberto Velasco was gunned down at his home in the capital May 6. He died in hospital shortly thereafter.
Since December 2006, Mexican President Felipe Calderon's government has deployed 36,000 military troops and thousands of police around the country in an operation aimed at clamping down on organized crime.
On Wednesday Mexican officials said police seized more than two tonnes of cocaine stashed in a house in the southeastern Mexican city of Tuxtla Gutierrez.