The State Department’s top diplomat for Latin American matters has resigned after a dispute with the White House over Guatemalan immigration policy, according to The Washington Post.

A senior administration official told the newspaper Kim Breier, assistant secretary of State for the Western Hemisphere, is leaving her post after White House policy adviser Stephen Miller Stephen MillerSpecial counsel investigating DeVos for potential Hatch Act violation: report Trump confirms another White House staffer tested positive for COVID-19 Biden pick creates furor, underscoring bitterness over Obama immigration policy MORE berated her in an email chain for what he perceived as an insufficient defense of the Trump administration’s “safe third country” asylum agreement with Guatemala.

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Miller told Breier that it was "her job" to defend the agreement, which requires Central American migrants to seek asylum in Guatemala before applying for asylum in the U.S., the official added. The Post notes that it is unclear whether this was a primary cause of her resignation.

A second senior official, however, told the newspaper no such email chain exists.

While other State Department officials, including Secretary of State Mike Pompeo Michael (Mike) Richard PompeoPutin nominated for Nobel Peace Prize The Hill's Morning Report - Sponsored by Facebook - Trump previews SCOTUS nominee as 'totally brilliant' Pompeo accused of stumping for Trump ahead of election MORE, have reportedly objected to the policy, Breier, a Mexico expert, primarily took issue with White House micromanagement, according to the Post, which cited officials.

Breier was reportedly a key figure in ongoing negotiations with Mexican officials, including talks in June that eventually averted threats by the White House to impose steep tariffs on Mexican goods. Mexican officials have remained in contact with her and see her exit as a major blow to relations, CNN reported, citing Mexican sources.

The State Department is expected to announce Breier’s resignation Thursday, but President Trump Donald John TrumpSteele Dossier sub-source was subject of FBI counterintelligence probe Pelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Trump 'no longer angry' at Romney because of Supreme Court stance MORE’s daughter Ivanka Trump Ivana (Ivanka) Marie TrumpThe Hill's 12:30 Report: Trump stokes fears over November election outcome Special counsel investigating DeVos for potential Hatch Act violation: report Trump, Biden vie for Minnesota MORE seemingly acknowledged her departure Wednesday night, tweeting, “While Jared [Kushner] and I will miss working with you, we are happy that Emma will now get to see more of the mom she is so proud of!”

Thank you @WHAAsstSecty Kim Breier for your friendship and great service. While Jared and I will miss working with you, we are happy that Emma will now get to see more of the mom she is so proud of! pic.twitter.com/7j8I6Kh5MT — Ivanka Trump (@IvankaTrump) August 8, 2019

Breier follows several other top diplomats who have left the State Department in 2019, including A. Wess Mitchell, her counterpart for European affairs, and policy planning head Kiron Skinner.

The Hill has reached out to the White House for comment. The State Department declined to comment.