Green Party nominee Jill Stein, contender in the recent US presidential election, and others are seeking an audit and recount of the voting results in Michigan, Pennsylvania and Wisconsin, CNN has reported.

This follows reports that voting security experts alerted Hillary Clinton's campaign to the possibility of hacks in key counties in those states, according to CNN.

President-elect Donald Trump claimed Pennsylvania and Wisconsin -- wins that helped push him comfortably over the threshold of 270 Electoral College votes needed for victory -- while Michigan remains too close to call, more than two weeks after Election Day.

But Clinton's lead in the popular vote has continued to grow -- she now has close to 2 million more votes than Trump -- and pressure has been mounting among liberals for an investigation into what happened on Election Day.