Solicitor General D John Sauer urged the Supreme Court to keep disputed ballots separate from valid ones, warning they could not be recovered once mixed. (EPA Images pic)WASHINGTON: The Trump administration asked the US Supreme Court on Monday to force California to set aside the mail-in ballots of more than 20,000 people it claims may not be American citizens.

The move, one day ahead of the crucial midterm elections, comes after lower courts last week rejected the demand by the department of justice (DOJ), with one judge calling it brazen pre-election "interference".

Solicitor general D John Sauer, in an emergency filing with the Supreme Court, said that "once California commingles the challenged ballots with lawful ones, there is no way to get the challenged ballots back."