A top member of US President Donald Trump's Republican Party, Senate Majority Leader Mitch McConnell, has congratulated Joe Biden on winning the presidential election last month
Senator McConnell spoke after the electoral college formally confirmed Biden's victory over Trump.
The Democrat won 306 electoral college votes to Trump's 232.
President Trump still refuses to concede, making unsubstantiated claims of widespread fraud.
Relations with the Senate, currently controlled by the Republicans, will be crucial to Biden's presidency.
On Tuesday, he travels to Georgia to campaign for the Democrats in next month's Senate run-off elections. Two seats will be decided on 5 January and could determine whether or not his party takes control of the chamber. Democrats already control the House of Representatives.
Speaking on the Senate floor, McConnell said: "Today I want to congratulate President-elect Joe Biden."
Also congratulating Biden's running-mate, Kamala Harris, he added: "All Americans can take pride that our nation has a female vice president-elect for the very first time."
President Trump does not appear to be changing his stance.
Tweeting on Tuesday, he said without offering evidence that "tremendous evidence" of voter fraud was "pouring in".
- BBC