Former National Security Advisor John Bolton is slated to testify on Thursday at President Donald Trump's impeachment inquiry, but will refuse, it has been claimed.

Democrats have called Bolton, along with 11 other witnesses, to closed-door interviews in the coming weeks.

The White House and Congress are locked in a legal battle over what right investigators have to compel witness testimony.

But despite reports Bolton was expected to appear, AXIOS reporter Jonathan Swan doused the suggestion on Monday night, tweeting: 'Bolton has no plans to testify, and nothing in his posture has changed, per source with direct knowledge.

'The committee can put him on the schedule but people shouldn't get too excited about that.'

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Former national security adviser John Bolton speaks to media at the White House in Washington in July

Speaker of the House Nancy Pelosi (left) who is leading the charge against President Doanld Trump

Asked whether Bolton should testify, Trump told reporters on Sunday: 'That's up to him and up to the lawyers.'

He added: 'I like John Bolton, I always got along with him.'

Democrats are heading into a crucial phase of their impeachment inquiry as they move toward public impeachment hearings this month.

This week they called Bolton, along with Energy Secretary Rick Perry to Capitol Hill. But it remains unclear whether they will attend.

Trump on Monday argued there was 'no reason to call witnesses' to testify on his phone call with the Ukrainian president.

'What I said on the phone call with the Ukrainian President is 'perfectly' stated. There is no reason to call witnesses to analyze my words and meaning. This is just another Democrat Hoax that I have had to live with from the day I got elected (and before!). Disgraceful!,' the president tweeted.

Four White House officials were summoned yesterday but declined to attend.

The four are leading a parade of officials who plan to skip their scheduled testimony on Capitol Hill this week as Democrats prepare to wrap up the closed-door testimony and begin public hearings in the coming weeks.

It's also a sign of increased stonewalling from the Trump administration after a string of witnesses on Capitol Hill revealed new details on the relationship between the U.S. and the Ukraine.

The impeachment inquiry began when a whistleblower flagged Trump's call to Zelensky where he asked the Ukraine to look into allegations that Joe Biden, as vice president, quashed a Ukrainian investigation into Burisma, where Biden's son Hunter served on the board from 2014 until earlier this year, and used the threat of withholding U.S. foreign aid.

Biden has denied any wrongdoing and no charges have been filed against either Biden.

Trump also has denied any wrong doing and said his call with Zelensky was 'perfect.'