US intelligence officials are examining an email account using a Russian internet domain as the potential source of non-credible bomb threats made on Election Day in the state of Georgia, sources familiar with the matter told CNN.

One US official told CNN that investigators believe at least some of the threats originated in Russia.

Email addresses can be spoofed and US officials have not yet confirmed that the emailed threats came from Russia, the sources said. However, investigators are looking at the history of the email account’s activity to try to determine who is behind the threats, the sources said.

The non-credible threats caused the temporary closure of polling places in Union City, just outside of Atlanta, according to Fulton County police.

“We’ve heard some threats that were of Russian origin,” Georgia Secretary of State Brad Raffensperger told reporters earlier Tuesday. The secretary did not elaborate on how exactly state officials determined the bomb threats came from Russia.