The Justice Department's top national security official is leaving her position next month.

Mary McCord told the staff of the department's national security division this week she's leaving to pursue other opportunities. Her departure comes as she is leading the department's investigation into whether President Donald Trump's campaign had ties to Russia's meddling in the 2016 election. And it creates a major vacancy at a time when several key positions within the department remain to be filled.

A longtime federal prosecutor, McCord had been acting as head of the national security division since October. The unit oversees cases involving terrorism, espionage, cyber and other national security threats.

In her memo, McCord did not reveal what she plans to do next, aside from spending time with her family.