More than 50 groups carrying the slogan "Stop the Steal" have popped up on Facebook in the last two days. The largest has drawn nearly 120,000 members.

The slogan is a reference to unsubstantiated claims by President Trump and some of his supporters that the election is being swung by "voter fraud".

One "Stop the Steal" group that attracted more than 360,000 members in a matter of hours was taken down by Facebook because of calls for violence.

Administrators of some of the new groups are warning their members to avoid using threatening or violent language.

Some have frequently changed their names, apparently in an attempt to avoid detection or removal by Facebook.

At least two "Stop the Steal" websites have also been created since election day to register volunteer activists, who are also trying to organise rallies in front of every US state capitol on Saturday.