WASHINGTON (AFP) - US Vice-President Mike Pence, in defiance of President Donald Trump, said on Wednesday (Jan 6) that he will not intervene to stop the certification by Congress of Democrat Joe Biden's election victory.

"The Constitution constrains me from claiming unilateral authority to determine which electoral votes should be counted and which should not," Pence said in a statement released as a joint session of Congress began to certify the Electoral College votes from the Nov 3 election.

Pence's statement was released as Trump urged the vice president at a rally in Washington to sign on to plans by some Republican lawmakers to object to the Electoral College results.

Pence, the presiding officer of the Senate, said he shared the "concerns of millions of Americans about the integrity of the election."

But the vice-president said he does not believe he has the "unilateral authority to decide which electoral votes should be counted."

"Four years ago, surrounded by my family, I took an oath to support and defend the Constitution, which ended with the words 'So Help me God," he said.

"Today, I want to assure the American people that I will keep the oath I made to them and I will keep the oath I made to Almighty God," he added.

At his rally, Trump repeated his baseless claims of election fraud and said he would be "very disappointed" if Pence failed to object to the Electoral College count.