US Democratic Senator Al Franken has announced his resignation, a day after a majority of his Democratic Senate colleagues called for him to step down following a string of sexual misconduct allegations against him.

Mr Franken, 66, a former comedian who had been seen as a rising star in the Democratic Party, announced his decision on the Senate floor.

"I know in my heart that nothing I've done as a senator - nothing - has brought dishonor on this institution," he said.

"Nevertheless, today I am announcing that in the coming weeks, I will be resigning as a member of the United States Senate."

Mr Franken is one of several prominent American men in politics, media and entertainment to be accused in recent months of sexual harassment and misconduct.

"Some of the allegations against me are simply not true. Others I remember very differently," he said.

The departure of the Minnesota Democrat presents an opening for Republicans to recapture a seat they lost when Mr Franken won election in 2008, and to build on their slim 52-48 Senate majority.

The election to succeed him, however, will not be held until November 2018. In the interim, Minnesota's Democratic governor, Mark Dayton, will appoint someone to take his place, ensuring Democrats hold the seat for now.

Allegations that Mr Franken had groped and tried to kiss women without their consent in the past began to surface three weeks ago.

After the initial accusations, Mr Franken said he was embarrassed and ashamed by his behavior but would not resign.

Rather, he said, he would cooperate with a Senate ethics probe and work to regain the trust of the people of Minnesota.

However, a majority of his Democratic Senate colleagues, including most of the party's female lawmakers in the chamber, pressed him to step down yesterday after a new allegation hit the news.

In putting pressure on Mr Franken to step aside, Democrats have tried to capture the moral high ground and draw a distinction between their party and Republicans.

Democrat John Conyers, the longest serving member of the US House of Representatives, stepped down last Tuesday after multiple accusations of sexual misconduct, the first member of Congress to leave his seat during the wave of high-profile harassment allegations.

Mr Conyers has denied the allegations against him.

Republican Roy Moore, who is running for the Senate in Alabama and who faces numerous accusations of sexual misconduct or assault, has been backed by President Donald Trump ahead of a special election next Tuesday.

Senate Republicans, however, have been cooler toward the candidate, who denies the accusations against him.