A lawyer for the whistleblower who raised alarms about US President Donald Trump’s dealings with Ukraine has said his client is willing to answer written questions submitted by House Republicans.

The surprise offer, made to Devin Nunes – the top Republican on the House Intelligence Committee – would allow Republicans to ask questions of the whistleblower without having to go through the committee’s chairman, Adam Schiff.

Mark Zaid tweeted that the whistleblower would answer questions directly from Republican members “in writing, under oath & penalty of perjury”, part of a bid to stem escalating efforts by Mr Trump and his Republican allies to unmask the person’s identity. He said only queries seeking the person’s identity will not be answered.

“Being a whistleblower is not a partisan job nor is impeachment an objective. That is not our role,” Mr Zaid tweeted. “So we have offered to @DevinNunes.”

“We will ensure timely answers,” he said.

The offer comes as Mr Trump has repeatedly demanded the release of the whistleblower’s identity, tweeting that the person “must come forward”.

The whistleblower raised concerns about Mr Trump’s July 25 call with Ukrainian President Volodymyr Zelenskiy, in which he pressed Mr Zelenskiy to investigate Mr Trump’s political rivals. That call became the catalyst for the impeachment inquiry.

The whistleblower’s second-hand 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.

“Reveal the Whistleblower and end the Impeachment Hoax!” Mr Trump tweeted.

Mr 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 first-hand 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,” Mr Trump told reporters at the White House. “And you know you’d be doing the public a service if you did.”

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