The Federal Bureau of Investigation is examining possible problems with postal ballots in the state of Pennsylvania, the Justice Department said in a press release on Thursday.
"On Monday, 21 September 2020, at the request of Luzerne County District Attorney Stefanie Salavantis, the Office of the United States Attorney along with the Federal Bureau of Investigation, Scranton Resident Office, began an inquiry into reports of potential issues with a small number of mail-in ballots at the Luzerne County Board of Elections," the release said.
The DoJ added that so far the investigation has uncovered only a small number of discarded ballots.
The FBI said in the release that it has conducted numerous interviews and reviewed certain physical evidence related to the matter, noting that Luzerne county has been cooperative.
Nine discarded military ballots - all cast for President Donald Trump - have been recovered, the FBI added.
The FBI also said that it will share more information related to its findings later on Thursday.
The US is due to hold a national presidential election on 3 November when Americans will choose electors who will, in turn, vote for one of the two major candidates - either Donald Trump, who is seeking re-election, or former Vice-President Joe Biden for whom this is his third attempt at presidency.
Several states have already launched early voting, both in person and by mail as the coronavirus pandemic has forced some people to avoid visiting polling stations - an idea supported by the Democrats.
President Trump, however, has repeatedly slammed the practice as leading to potential electoral fraud.