By Dustin Volz

WASHINGTON (Reuters) – U.S. Department of Homeland Security employees in the Washington area were unable to access some agency computer networks on Tuesday, according to three sources familiar with the matter.

It was not immediately clear how widespread the issue was or how significantly it affected daily functions at DHS, a large government agency whose responsibilities include immigration services, border security and cyber defense.

Employees began experiencing problems logging into networks at 5 a.m. ET on Tuesday due to a problem related to the personal identify verification (PIV) cards used by federal workers and contractors to access certain information systems, one source said. At least four DHS buildings were affected, the source said, including locations used by U.S. Citizenship and Immigration Services.

Another source said the cards did not appear to be responsible. DHS did not immediately respond to requests for comment.

President Donald Trump vowed to make cyber security a priority during his administration, following an election marred by hacks of Democratic Party emails that U.S. intelligence agencies concluded were carried out by Russia in order to help Trump, a Republican, win. At a White House event last month he said he would “hold my Cabinet secretaries and agency heads accountable, totally accountable, for the cyber security of their organizations.”

Trump had planned to sign a cyber security executive order last month but it was put on hold to allow more time for review.

(Reporting by Dustin Volz; Editing by Jonathan Oatis)