The US ambassador to Mexico has resigned after a public dispute with President Felipe Calderon over the handling of the war against Mexico's powerful drug gangs.
US Secretary of State Hillary Clinton said on Saturday that she and President Barack Obama had accepted Ambassador Carlos Pascual's resignation "with great reluctance."
The announcement came as a surprise just as Obama began a five-day trip to Latin America, where he is visiting El Salvador, Brazil and Chile, to shore up ties with the region.
The United States and Mexico have long lauded their close economic ties and cooperation on security issues, with more than $1 billion in US aid being funneled to Mexican forces to battle the drug cartels.
But a diplomatic fight erupted after State Department documents published by WikiLeaks showed Pascual criticizing Mexican authorities' lack of coordination in operations targeting cartel leaders.
Calderon lashed out in an unusually critical newspaper interview on Feb. 22, saying Pascual had shown "ignorance" and distorted what was happening in the country.
He also said US security forces failed to coordinate their own efforts and saw each other as "rivals."
Calderon is facing increasing pressure in Mexico over his security strategy as the death toll from drug violence has climbed to more than 36,000 since he took office in late 2006.
In a visit to Washington earlier this month, Calderon reportedly requested that Pascual be removed from his post.
Pascual decided to resign "to avert issues raised by President Calderon that could distract from the important business of advancing our bilateral interests," Clinton said on Saturday.
Mexico and the United States trade more than $1 billion a day across their long border and in recent years stepped up intelligence sharing in operations to bring down major drug traffickers.
Calderon's office on Saturday said U.S.-Mexico relations remained solid despite Pascual's resignation and the two nations would continue working together to deepen their relationship "as neighbors and friends."
But the alliance has recently been soured by the public dispute between Calderon and Pascual and Washington's failure to stop weapons smuggling into Mexico.
A decision to allow unmanned surveillance drones to fly over Mexican territory has drawn criticism, with opposition politicians saying it violates Mexico's sovereignty. The killing of a U.S. immigration official in a suspected drug cartel ambush last month also raised tensions.
Pascual, a Cuban-born career diplomat with more than two decades of service, recently began dating the daughter of a senior figure inside Mexico's main opposition Institutional Revolutionary Party, or PRI.
Calderon's conservative National Action Party (PAN) is struggling in polls ahead of a presidential election next year and the relationship may have raised concerns inside his team.
A cable signed by Pascual in 2009 remarked "the PRI party is in the ascendancy," and called PAN's prospects of winning the election "bleak."