"We believe this activity was linked to the incidents, connected to the executive office of the president a few weeks ago," a spokesperson for the Department of State Jeff Rathke said Monday.
The State Department declined to apportion blame, saying the "origins of the intrusion is something that remains under investigation."
The breach targeted the State Department's unclassified email system several weeks ago, the State Department said. No classified systems were targeting or breached. As a security precaution, systems connecting the department's email to the internet have been temporarily shut down. The department's internal email system is still running.
The State Department's announcement comes as a number of US government offices have been targeted by hackers. In addition to the breach of the White House's unclassified system in October, US Postal Service said hackers breached its personal data information last week. In September, systems belonging to the US National Oceanic and Atmospheric Administration were also breached.