WASHINGTON (Reuters) - Loophole-laden laws in the United States are hampering efforts to stop the gun smuggling that fuels Mexico’s drug-related violence, according to a congressional report released on Thursday.

A Eubank 7.69x39 sits in front of AK-47s confiscated in crimes, some that have been smuggled into Mexico, are stored in one of the "vaults" at the local office of the ATF (Bureau of Alcohol, Tobacco and Firearms) as evidence for trial or waiting to be melted down in Phoenix, Arizona, July 6, 2007. REUTERS/Jeff Topping

Efforts to trace firearms seized in Mexico are delayed by an average of two weeks due to the absence of a national U.S. firearms registry, the Government Accountability Office said.

The report was released as the Obama administration tries to step up efforts to intercept the flow of cash and guns south to Mexico as part of its anti-drug strategy.

Drug-related violence killed more than 6,300 in Mexico last year, and authorities say that 90 percent of the guns seized from drug cartels in the past three years that could be traced came from the United States.

“It is simply unacceptable that the United States not only consumes the majority of the drugs flowing from Mexico, but also arms the very cartels that contribute to the daily violence that is devastating Mexico,” said Democratic Representative Eliot Engel, who chairs the congressional subcommittee that commissioned the report.

The report also found that the lack of a paper trail for firearms sold at gun shows and pawn shops slowed down investigators as they tried to crack gun-smuggling networks.

When investigators finally establish where a gun was purchased the trail has often gone cold because smuggling networks shift personnel frequently, congressional researchers wrote.

The U.S. Homeland Security Department in April announced plans to spend $400 million on scanners and other equipment to detect arms shipments headed south.

U.S. border guards in recent years have not made weapons inspections a priority, with only 35 southbound weapons seizures involving a total of 70 weapons in fiscal 2008, the report said.

The administration’s new border strategy also emphasizes cooperation among different law enforcement agencies, but the report said the two agencies primarily responsible for fighting gun-running -- Immigration and Customs Enforcement (ICE) and the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) -- had not consistently coordinated their efforts.

The Homeland Security Department, which oversees ICE, disputed that assessment but said the two agencies are working on an agreement that will allow them to work more closely together. ATF falls under the Justice Department.

Homeland Security also announced Thursday that its customs agency had reached an agreement with the Drug Enforcement Administration that will allow more customs agents to target drug smugglers.