The Latest: Nielsen supports Trump's goal of securing border

WASHINGTON (AP) -- The Latest on the departure of Homeland Security Secretary Kirstjen Nielsen (all times local):

12:45 p.m.

Kirstjen (KEER'-sten) Nielsen says she continues to support President Donald Trump's goal of securing the U.S.-Mexico border in her first public remarks since her surprise resignation as Homeland Security secretary.

Nielsen told reporters gathered outside her Alexandria, Virginia, home on Monday that she will keep supporting "all efforts to address the humanitarian and security crisis" on the border.

Nielsen thanks the Republican president for "the tremendous opportunity to serve this country." She says she's spent the last 24 hours talking to administration officials and members of Congress to ensure a smooth transition and intends to continue "to support" the department "from the outside."

Nielsen resigned Sunday amid Trump's growing frustration and bitterness over a spike in Central American migrants crossing the border.

Customs and Border Protection Commissioner Kevin McAleenan has taken over as department head.

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12:55 a.m.

Homeland Security Secretary Kirstjen Nielsen has resigned amid President Donald Trump's growing frustration and bitterness over the number of Central American families crossing the southern border.

Trump announced on Sunday in a tweet that U.S. Customs and Border Protection Commissioner Kevin McAleenan would be taking over as acting head of the department. McAleenan is a longtime border official who is well-respected by members of Congress and within the administration. The decision to name a top immigration officer to the post reflects Trump's priority for the sprawling department founded to combat terrorism following the Sept. 11 attacks.

Though Trump aides were eyeing a staff shake-up at Homeland Security and had already withdrawn the nomination for another key immigration post, the development Sunday was unexpected.