The US ambassador to Mexico has resigned amid a furore over a leaked diplomatic cable in which he complained about inefficiency and infighting among Mexican security forces in the campaign against drug cartels.
Hillary Clinton said Carlos Pascual's decision to step down was "based upon his personal desire to ensure the strong relationship between our two countries and to avert issues" raised by the Mexican president, Felipe Calderon.
The US secretary of state was not specific, but a furious Calderon has publicly criticised Pascual's criticisms, divulged as part of the US embassy cables by WikiLeaks.
Pascual's resignation appears to be the biggest fallout yet from the release of thousands of sensitive US diplomatic cables from around the world. It is the first such public departure by a US ambassador during the Obama administration.
Clinton went to lengths to praise Pascual's work in Mexico and said the Obama administration never lost confidence in him. Clinton said Pascual's work with Mexico to build institutions capable of fighting drug traffickers "will serve both our nations for decades".
She was "particularly grateful to Carlos for his efforts to sustain the morale and security of American personnel after tragic shootings in Mexico" that killed a US employee and three other people tied to the consulate in the border city of Ciudad Juarez last year.
"It is with great reluctance that President Obama and I have acceded to Carlos's request" to step down, Clinton said in a statement.
The ambassador's resignation laid bare how difficult relations between the US embassy and the Mexican government had become since the release of the cable in December. Calderon has made no secret of his personal anger at Pascual.
"I will not accept or tolerate any type of intervention," Calderon said in an interview with the newspaper El Universal in late February. "But that man's ignorance translates into a distortion of what is happening in Mexico and affects things and creates ill feeling within our own team."
There was no immediate reaction from the Mexican government, although an official from Calderon's office said it was preparing a response.
Pascual may have ruffled feathers in the Mexican government and Calderon's National Action party by dating the daughter of Francisco Rojas, the congressional leader of the former longtime ruling Institutional Revolutionary Party. Mexican officials and the U.S. Embassy have declined to comment on that matter.
One of the leaked diplomatic cables that most angered Calderon referred to friction between Mexico's army and navy while detailing an operation that led to the death of drug lord Arturo Beltran Leyva.
Pascual said the US, which had information locating Beltran Leyva, originally took it to the army, which refused to move quickly. Beltran Leyva was eventually brought down in a shootout with Mexican marines, who have since taken the lead in other operations against cartel capos.
Other cables reported jealousies and a lack of co-ordination between various Mexican security forces.