Secretary of State Mike Pompeo is in quarantine after being exposed to someone who tested positive for coronavirus, according to a State Department spokesperson.

It’s unclear when or where the top U.S. diplomat was exposed or by whom, a detail the State Department said it won’t confirm for privacy reasons. But he has tested negative and remains under monitoring by the department’s medical team, the spokesperson said.

Pompeo was scheduled to deliver remarks at a holiday reception for U.S. diplomats in dangerous posts and their families Tuesday, but did not show up, according to two State Department sources.