WASHINGTON (Reuters) — U.S. officials said late Friday that Iranian hackers behind the threatening emails sent to thousands of Americans earlier this month successfully accessed voter data.

The FBI and the Department of Homeland Security, in a joint statement, confirmed that “the actor successfully obtained voter registration data in at least one state.”

The state was not identified. The FBI and DHS did not immediately return messages.

U.S. officials have been on high alert over the threat of potential cyber interference in the upcoming Nov. 3 election, which pits Republican President Donald Trump against Democratic challenger Joe Biden.

This is a developing story.