Bipartisan members of the Senate’s lead probe into alleged Russian meddling in the 2016 presidential election are clamoring for the testimony of President Donald Trump’s eldest son into new revelations that he meet last year with a Kremlin-linked lawyer — a meeting he has denounced as a “big yawn.”

On Monday, lawmakers returned from their Independence Day recess to Capitol Hill to reports, later confirmed by the president’s son., of what appeared to be the first confirmed private meeting between members of then-candidate Trump’s inner circle and Russians with Kremlin ties.

The June 9, 2016, meeting occurred at New York’s Trump Tower two weeks after Mr. Trump secured the Republican nomination and included Mr. Trump Jr.; Mr. Trump’s son-in-law Jared Kushner, now a top White House adviser; and Mr. Trump’s then-campaign chairman, Paul Manafort. The three met with Russian lawyer Natalia Veselnitskaya.

Reportedly active in a campaign by the Russian government to overturn the Magnitsky Act, a law U.S. Congress passed in 2012 that withholds visas and freezes the financial assets of Russian officials accused of human rights violations, Ms. Veselnitskaya claimed to have damaging information about Democratic nominee Hillary Clinton.

The circumstances surrounding the meeting, and a report by The New York Times late Monday that Mr. Trump Jr. was told ahead of time that the source of the information was the Russian government, fueled new questions about the Trump campaign’s possible ties to Moscow, which are being scrutinized by federal and congressional investigators, The Associated Press said.

The Times reported that Mr. Trump Jr., who was a key campaign adviser to his father, was told the Russian government was behind the information on Clinton in an email from music publicist Rob Goldstone. The Times cited three unnamed people with knowledge of the email.

The report is the first public word that Mr. Trump Jr. accepted the meeting with the understanding that he would be presented with damaging information about his father’s political opponent and that the material could have emanated from the Kremlin.

Senate Intelligence Committee member Sen. Susan Collins, a Maine Republican, told reporters Monday on Capitol Hill the panel “needs to interview him [Donald Trump Jr.] and others who attended the meeting.”

Rhode Island Democrat, Sen. Jack Reed, who sits on the Intelligence committee as an “ex officio” member, supported calls for more details.

“I think it’s appropriate that [Donald Trump Jr.] does that to clear this up,” Mr. Reed added.

Mr. Trump Jr. and the White House spent the day pushing back against allegations of any wrongdoing. “Happy to work with the committee to pass on what I know,” he tweeted in response to the Senate’s desire to meet him. He also retweeted a New York Post opinion piece calling the story a “big yawn.”

Mr. Trump Jr. has also explained that he didn’t know the identity of whom he was meeting that June day and that when he finally met Ms. Veselnitskaya — “her statements were vague, ambiguous and made no sense.”

“Obviously I’m the first person on a campaign to ever take a meeting to hear info about an opponent… went nowhere but had to listen,” Mr. Trump Jr. tweeted sarcastically.

In the background of the June meeting, Russian hackers were also allegedly attacking the Democratic National Committee computer network.

White House adviser Kellyanne Conway said Monday that the meeting proved nothing. “No information was received that was meaningful or helpful, and no action was taken,” she said on CNN. Deputy Press Secretary Sarah Huckabee Sanders also said the meeting presented no evidence of collusion between the Trump campaign and Russia.

It was “a very short meeting of which there was absolutely no follow-up,” Ms. Huckabee Sanders said.

In Moscow on Monday, Kremlin spokesman Dmitry Peskov denied that the Russian government knew a Russian lawyer named Natalia Veselnitskaya.

“No, we don’t know who it is and, certainly, we cannot track down all movements of all Russian lawyers both within Russia and abroad,” Mr. Peskov said.

Multiple congressional committees and a Department of Justice special counsel, Robert Mueller, are investigating whether Russia interfered in the election and colluded with the Trump campaign.

On Sunday, the House Intelligence Committee’s ranking Democrat Rep. Rep. Adam Schiff, added his committee needed to “get to the bottom” of the meeting.

Meanwhile Senate Intelligence Committee staffers will have their first interviews with Trump campaign officials this week, according to a source familiar with the interview process.

No names have been released — but the committee has expressed a desire to hear from both Mr. Kusher and Mr. Manafort and has already heard testimony from Attorney General Jeff Sessions and former FBI Director James B. Comey.

• This article was based in part on wire service reports.

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