(Updates with further Zuckerberg comments, adds share price graphic)
WASHINGTON/SAN FRANCISCO, April 10 (Reuters) - Facebook Inc shares posted their biggest daily gain in nearly two years on Tuesday as Chief Executive Mark Zuckerberg fended off questions from U.S. senators on how the world's largest social network might be regulated more closely.
Zuckerberg repeated apologies made on Monday for a range of problems that have beset Facebook, from data privacy to foreign attempts to influence U.S. elections, but the 33-year-old internet mogul managed to deter any specific talk about new laws and made no new promises.
"Ill have my team follow up with you so that way we can have this discussion across the different categories where I think this discussion needs to happen," Zuckerberg told a joint hearing by the U.S. Senate's Commerce and Judiciary committees, when asked what regulations he thought were necessary.
He denied that Facebook, which has more than 2 billion monthly users across the world, was a monopoly. "It certainly doesn't feel that way to me," Zuckerberg said.
Wearing a dark suit and tie instead of his typical T-shirt and jeans, Zuckerberg appeared largely unruffled as senators questioned him. Investors welcomed his performance.
"Zuckerberg is conciliatory in his presentation," said Mariann Montagne, portfolio manager at Gradient Investments in Arden Hills, Minnesota. "The stock is running up on his comments. Maybe people like seeing Zuckerberg in a suit.
Facebook shares closed up 4.5 percent at $165.04, their highest level in almost three weeks. It was their largest daily gain since April 28, 2016.
The shares fell steeply last month after it came to light that millions of users' personal information was harvested from Facebook by Cambridge Analytica, a political consultancy that has counted U.S. President Donald Trump's election campaign among its clients. The latest estimate of affected users is up to 87 million.
CRISIS OF CONFIDENCE
That disclosure pitched Facebook into a crisis of confidence among users, advertisers, employees and investors who were already struggling with Facebook's reaction to fake news and its role in the 2016 election.
Facebook disclosed in September that Russians under fake names used the social network to try to influence U.S. voters in the months before and after the 2016 election, writing about inflammatory subjects, setting up events and buying ads.
We believe it is entirely possible that there will be a connection there, Zuckerberg said when asked if there was overlap between Cambridge Analyticas harvested user data and the political propaganda pushed by the Kremlin-linked Internet Research Agency during the 2016 presidential election, which Facebook has said was seen by some 126 million people.
In February, U.S. Special Counsel Robert Mueller, who is investigating possible links between Russia and Trump's campaign, charged 13 Russians and three Russian companies with interfering in the election by sowing discord on social media.
On Tuesday, Zuckerberg said he believed Facebook employees have been interviewed by Mueller's office.
Zuckerberg, who founded Facebook in his Harvard University dorm room in 2004, is fighting to prove to critics that he is the right person to go on leading what has grown into one of the world's largest companies.
On Friday, Zuckerberg threw his support behind proposed legislation requiring social media sites to disclose the identities of buyers of online political campaign ads.
(Reporting by Dustin Volz in Washington and David Ingram in San Francisco; Additional reporting by David Shepardson and Andy Sullivan in Washington, April Joyner and Lewis Krauskopf in New York; Writing by Bill Rigby; Editing by Meredith Mazzilli and Peter Cooney)