Vince Cable has insisted that both he and Nick Clegg were "absolutely" unaware of allegations that their party chief Lord Rennard sexually pestered female staff.
Despite claims that senior party figures were told of concerns about Lord Rennard as far back as 2008, Dr Cable insisted he was not aware of speculation about the peer's behaviour.
The Liberal Democrat Business Secretary promised the party will now get to the bottom of accusations from "distressed" women about the behaviour of Lord Rennard, a former chief executive.
Speaking on the BBC's Andrew Marr Show, Dr Cable also urged people not to "jump to conclusions" before the party's investigations have run their course.
He said there will be two inquiries into the party's handling of complaints and the allegations themselves, which are strongly denied by Lord Rennard.
Both Tim Farron, the Liberal Democrat president, and Tim Gordon, the chief executive, will look into the "serious" matter, he said.
Dr Cable said he was "absolutely not" aware of any allegations about Lord Rennard and he believes Mr Clegg knew nothing as well.
"They are serious and we take them very seriously," he said. "It's obviously wrong if there are women who have made complaints, felt they haven't dealt with them properly, so we are now setting up a proper investigative process, we want an independent element to that and get to the bottom of it."
It comes after fresh allegations that Jo Swinson, the business minister, and even Nick Clegg himself, may have been aware of women claiming to have been harrassed by Lord Rennard in 2009.
The Mail on Sunday published a Facebook discussion of the claims from January 2009 in which one party worker wrote: "I just don't know how nick can know and not do anything".
The Telegraph also revealed on Friday that Nick Clegg's most senior aide was told almost three years ago about allegations that a senior party figure had repeatedly sexually pestered female staff.
Mr Clegg's aides deny that he knew anything about accusations against Lord Rennard. Miss Swinson has also released a statement saying she "took action and ensured that others took action" when she was told about complaints by potential female Liberal Democrat candidates.
Lord Rennard has now stepped aside from his role as a senior Liberal Democrat policy adviser to fight the allegations that he sexually pestered female staff.
The top Lib Dem official stood down from his party duties to avoid "embarrassment" to the party, after several women made accusations about his conduct on Channel Four News this week.
The peer resigned from his role as chief executive in 2009 but was still actively involved in the Liberal Democrats. He will now withdraw from the party's group in the House of Lords, which means he will not be able to vote with his party on any issues.
He will also leave from the party's federal policy committee, which is responsible for coming up with ideas for the Liberal Democrat manifesto.
Lord Rennard faces "disciplinary procedures" after former party staff reported that he behaved inappropriately towards them at party events.
Once the party’s electoral mastermind, Lord Rennard oversaw a number of successful by-election campaigns, as well as the 2001 and 2005 general election campaigns.
He quit his post in 2009 for “family and health reasons” but remains active in the party and regularly attends its events.
Several Lib Dem women told Channel Four News on Thursday that while he was chief executive, Lord Rennard had touched them inappropriately or propositioned them.
Bridget Harris, a former special adviser to Mr Clegg, said that in a hotel bar at a party conference, the peer repeatedly touched her legs without permission.
“I had to physically move away from him,” she said. “He suggested that we take our coffees upstairs to his room.”
Mrs Harris said she reported the incident to party managers, but nothing was done.
Another, anonymous, Lib Dem woman, told the channel that the peer once “shoved his hand down the back of my dress”.
An internal Lib Dem email seen by Channel Four News also referred to several other allegations of inappropriate behaviour that were known to senior Lib Dem politicians.
Lawyers for Lord Rennard told Channel Four News: "Lord Rennard has always strived to conduct himself responsibly and appropriately at all times and has no recollection of any inappropriate behaviour.
"In addition, our client is unaware of any complaint about his conduct ever being made against him... In addition, Lord Rennard describes as completely untrue, any suggestion that he resigned as chief executive as a result of allegations about inappropriate behaviour.”
Before his resignation, it emerged that Lord Rennard had claimed more than £40,000 for a second home, despite owning an apartment less than two miles from Westminster. A Lords inquiry found his claims were in keeping with the rules at the time.