The United States Vice President Mike Pence has rejected President Donald Trump's demand that he blocks the confirmation of Joe Biden's election as the next president by Senate.

Pence said in a letter that he did not believe that as vice president he has the unilateral power to accept or reject electoral votes.

"Some believe that as Vice President, I should be able to accept or reject electoral votes unilaterally. Others believe that electoral votes should never be challenged in a Joint Session of Congress. After a careful study of our Constitution, our laws, and our history, I believe neither view is correct," said Pence.

President Trump held a rally on Wednesday outside the White House, where he called again upon Pence to block Biden's confirmation.

"Mike Pence, I hope you're gonna stand up for the good of our Constitution and for the good of our country, and if you're not I'm gonna be very disappointed in you, I will tell you right now," he said.

In his letter however, Pence pointed to the country's constitution as his guiding authority on the matter.

"It is my considered judgement that my oath to support and defend the Constitution constrains me from claiming unilateral authority to determine which electoral votes should be counted and which should not," he said.

"When the Joint Session of Congress convenes today, I will do my duty to see to it that we open the certificates of the Electors of the several states, we hear objections raised by Senators and Representatives, and we count the votes of the Electoral College for President and Vice President in a manner consistent with our Constitution, laws, and history."