Inquiry into US anti-gun trafficking operation ordered
US Attorney General Eric Holder has asked a top federal official to review efforts by US agents to hunt gun traffickers along the US-Mexico border.
The move comes amid reports that a US federal operation that allowed weapons to pass into the hands of suspected gun smugglers has lost hundreds of guns.
Some of those firearms have been indirectly linked to the shooting of a US Border Protection agent in Arizona.
The agency in charge of the programme has also launched its own review.
The US Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) was in control of the programme, known as Operation Fast and Furious, which funnelled weapons to suspected gun smugglers in the hope of tracking the firearms to alleged drugs gang leaders in Mexico.
The ATF announced on Thursday that it would ask a panel of law enforcement professionals to review the bureau's firearms trafficking strategies, in addition to the federal probe.
Its gun trafficking operation was conducted despite suspicions by US authorities that the firearms could be used to commit crimes, the Washington Post newspaper reported, citing federal sources.
The ATF allowed about 1,765 firearms over the span of 15 months to pass from gun dealers to buyers suspected of involvement in gun smuggling, the Center for Public Integrity reported.
And of those guns, 797 were recovered in both the US and Mexico, the non-partisan research group said.
At least 195 of the guns involved have been linked to some form of crime or law enforcement action, according to documents obtained by the Center for Public Integrity.
The ATF told the Washington Post its agents had taken every possible precaution to ensure that guns were recovered before they crossed into Mexico.
The BBC's Andrew North in Washington says the operation was kept secret from the Mexican government, which has long pressed the US authorities to do more to stop weapons smuggling across the border.
A spokesman for the Mexican embassy in Washington told the BBC: "Mexico has underscored the need for US law enforcement agencies to significantly deter the trafficking of guns into Mexico.
"We will continue to encourage more aggressive interdiction efforts on the US side of the border."
US agent death
Two of the weapons used in the ATF operation were found at the scene of a gunfight that killed US Customs and Border Protection agent Brian Terry in December.
No-one has been charged in Mr Terry's shooting, and the ATF has said there is no evidence proving the Fast and Furious weapons found at the scene were used in the shooting.
Senator Chuck Grassley, the senior Republican member of the Senate Judiciary Committee, has set up an inquiry to determine whether the weapons used in Operation Fast and the Furious crossed the border inadvertently or were deliberately spread to areas of Mexico by US law enforcement.
He questioned whether weapons sold to suspected "straw purchasers" were then tracked adequately by the ATF.
The justice department turned down a request by Mr Grassley for copies of communications between the ATF headquarters in Washington and the organisation's office in Phoenix in Arizona after Mr Terry was killed.
"We are not in a position to disclose documents relating to any ongoing investigation," the justice department told Mr Grassley.
The ATF said it believed its review would enhance its effectiveness when engaging in complex weapon trafficking investigations in the future.