As millions of people cast their ballots in the US election, claims have been spreading online questioning the integrity of the vote.

Election officials have been quick to reject some accusations of voting malpractice, as well as clarifying some legitimate problems which have been taken out of context.

BBC Verify is tracking and investigating the most widely shared claims – here’s four.

An image on social media shows a person holding a mail-in ballot paper which already had a mark next to Kamala Harris’s name.

The person who posted it on X claims that voting for anyone else would render the ballot void.

One post, viewed more than 3 million times, said the picture showed “weird ballot shenanigans happening”.

BBC Verify spoke to the Kentucky Board of Elections which rejected the allegation.

It said it had mailed out 130,000 ballots so far and had not been made aware of any complaints about mail-in ballots having pre-printed marks in any candidate selection boxes.

“As no one has presented a pre-marked ballot to election administrators or law enforcement, the claim that at least one ballot may have had a pre-printed mark in Kentucky, currently only exists in the vacuum of social media,” it said.

The election board added that for mail-in ballots in Kentucky if more than one candidate choice is marked in ink, then the ballot will still be counted if the voter circles their preferred choice.

A post on X which claims “the Pentagon reportedly failed to send absentee ballots to active military service members before the election” has been viewed over 28 million times.

It references a letter to Secretary of Defence Lloyd Austin, written by three Republican members of congress, expressing “grave concern” over “deficiencies” in procedures for overseas military personnel to vote.

However the letter does not accuse the Pentagon of failing to send them absentee ballots.

It is not the Pentagon’s job to do this – military personnel can vote abroad through the Federal Voting Assistance Program (FVAP) and ballots are sent to them by election officials where they are registered in the US.

If the ballot is in danger of not arriving before the voting deadline, personnel can vote via what is called a Federal Write-In Absentee Ballot (FWAB).

The letter claims an unspecified number of “service members” had requested a FWAB but were told their base had run out. However, it is possible to download and sign one through the FVAP website.

We asked the Department of Defense for details about how many people had been affected by the issue, but it would not comment. It did say that it had trained 3,000 Voting Assistance Officers to support personnel with voting.

Officials in the US state of Pennsylvania have rejected claims that “illegal voters” were able to apply for ballots and vote at an election office in Allegheny County.

They released a statement after posts on X went viral, claiming to show “illegal voters” being guided past US voters who had been waiting in line.

A video which appears to show someone repeatedly trying and failing to vote for Donald Trump on a voting machine in Laurel County, Kentucky – before a vote appears next to Kamala Harris’s name – has gone viral.

The person posting it says: “I hit Trump’s name 10 times and it wouldn’t work I then began recording and you can see what happened…. Switched it to Harris.”

Another post, viewed nearly seven million times, features the video with the claim: “Voting machines in Kentucky are literally changing the vote from Donald Trump to Kamala Harris. This is election interference!”

Election officials confirmed the video was authentic and the machine did malfunction, but said it was an isolated incident and the voter was able to cast their ballot as intended.

“After several minutes of attempting to recreate the scenario, it did occur. This was accomplished by hitting some area in between the boxes. After that we tried for several minutes to do it again and could not,” the county clerk said in a statement.

The machine in question was taken out of action until it was inspected, and later in the day the county clerk posted a video on Facebook showing the machine working correctly.

“In an election on this scale there are always going to be some problems,” said Joseph Greaney, a voting expert at US election website Ballotpedia.

“It can be one or two machines but people are extrapolating those out into a bigger problems, but I would say with a good degree of confidence that they are isolated incidents and they are caught,” he added.