WASHINGTON (AP) — The whistleblower who raised alarms about President Donald Trump's dealings with Ukraine and touched off the Democratic-led impeachment inquiry is willing to answer written questions submitted by House Republicans, the person's lawyer says.

The offer made over the weekend to Rep. Devin Nunes, the top Republican on the intelligence committee, was aimed in part at fending off escalating attacks by Trump and his GOP allies who are demanding the whistleblower's identity be revealed.

It would allow Republicans to ask questions of the whistleblower without having to go through the committee's chairman, Rep. Adam Schiff, D-Calif.

"Being a whistleblower is not a partisan job nor is impeachment an objective. That is not our role," Mark Zaid, the whistleblower's attorney, tweeted Sunday.

"We will ensure timely answers," he said.

Zaid said the whistleblower would answer questions directly from Republican members "in writing, under oath & penalty of perjury." Only queries seeking the person's identity won't be answered, he said.

Nunes' office did not have immediate comment.

The surprise proposal comes as Trump stepped up attacks on the whistleblower as lacking credibility, tweeting Sunday that the person "must come forward." The whistleblower raised concerns about Trump's July 25 call with Ukrainian President Volodymyr Zelenskiy, in which he pressed Zelenskiy to investigate Trump's political rivals.

The whistleblower's secondhand account of the call has been providing a road map for House Democrats investigating whether the president and others in his orbit pressured Ukraine to probe political opponents, including former Vice President Joe Biden.

Democrats are heading into a crucial phase of their impeachment inquiry as they aim to move toward public impeachment hearings later this month. In the coming week, they have called in 11 witnesses, including Energy Secretary Rick Perry and former national security adviser John Bolton for closed-door interviews. It's unclear whether any of them will come to Capitol Hill.

"Reveal the Whistleblower and end the Impeachment Hoax!" Trump tweeted Sunday.

Trump later pushed the news media to divulge the whistleblower's identity, asserting that the person's accounting of events is incorrect. The whistleblower's complaint has been corroborated by people with firsthand knowledge of the events who have appeared on Capitol Hill.

"They know who it is. You know who it is. You just don't want to report it," Trump told reporters at the White House. "And you know you'd be doing the public a service if you did."

U.S. whistleblower laws exist to protect the identity and careers of people who bring forward accusations of wrongdoing by government officials. Lawmakers in both parties have historically backed those protections.

The Associated Press typically does not reveal the identity of whistleblowers.

The whistleblower has become a central fixation for Republicans, and in particular the president. Republicans view a political opportunity in unmasking the CIA official, whom the intelligence community's inspector general said could have "arguable political bias." The inspector general nevertheless found the whistleblower's complaint to be "credible."

The president believes that if he can expose bias in the initial allegations against him, he can paint the entire impeachment inquiry it launched as a partisan, political probe. To this point, Republicans have largely fought the impeachment inquiry on process, not substance, believing it was tainted because interviews were conducted in closed sessions — ignoring that GOP lawmakers were in attendance — and complaining that House Speaker Nancy Pelosi had not called a vote to launch the matter.

But Pelosi called such a vote last week and the inquiry will soon shift into open hearings. Now, Trump is demanding that his allies defend his actions, insisting that he did nothing wrong while arguing that quid pro quos like the one allegedly offered Ukraine are common occurrences while leveraging power in conducting foreign policy.

House Minority Leader Kevin McCarthy, R-Calif., said Sunday that he had not yet discussed the whistleblower's offer with Nunes, but stressed that the person should answer questions in a public appearance before the committee.

"When you're talking about the removal of the president of the United States, undoing democracy, undoing what the American public had voted for, I think that individual should come before the committee," McCarthy told CBS' "Face the Nation."

"We need an openness that people understand this," he added.

Zaid said his team had addressed the issue of alleged bias with Republican members of the committee and had stressed the need for anonymity to maintain the safety of the whistleblower and that person's family, "but with little effect in halting the attacks."

"Let me be absolutely clear: Our willingness to cooperate has not changed," tweeted Andrew P. Bakaj, another attorney representing the whistleblower. "What we object to and find offensive, however, is the effort to uncover the identity of the whistleblower."

Bakaj wrote on Saturday that "their fixation on exposing the whistleblower's identity is simply because they're at a loss as to how to address the investigations the underlying disclosure prompted."

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Associated Press writer Jonathan Lemire in New York contributed to this report.