Former national security adviser John Bolton will not voluntarily testify in the impeachment inquiry against President Donald Trump, according to his lawyer.
The House committees leading the impeachment investigation have asked Mr Bolton to appear behind closed doors next week.
However, his lawyer Charles Cooper said Mr Bolton will not appear without a subpoena.
The inquiry wants to hear from Mr Bolton after other witnesses told them of his concerns with President Trump's dealings in Ukraine and the backchannel activities of Rudy Giuliani, Mr Trump's personal lawyer.
Mr Bolton was ousted by Mr Trump from his position as national security adviser in September.
Meanwhile Tim Morrison, President Trump's top adviser for Russian and European affairs, is due to testify in the inquiry on Thursday.
On Wednesday a senior administration official said Wednesday that Mr Morrison "has decided to pursue other opportunities".
It comes as the House prepares to take its first official vote Thursday on the process ahead. That includes public hearings in a matter of weeks and the possibility of drafting articles of impeachment against the president.
The White House has urged officials not to testify in the impeachment proceedings.
It is not guaranteed that those called will appear for depositions, even if they receive subpoenas as previous witnesses have.
Reporting by agencies.
