US House investigators have asked former National Security Adviser John Bolton to testify in their impeachment inquiry of President Donald Trump, deepening their reach into the White House as the probe accelerates towards a potential vote to remove the president.
House of Representatives investigators have invited him to appear next month.
Mr Trump has denied using the power of his office to pressure Ukraine to investigate former US Vice-President Joe Biden and his son.
Mr Bolton likened the alleged proposal to a “drug deal”, according to witness testimony.
It is unclear if Mr Bolton, who left his position in September after falling out of favour with the president, will appear as scheduled on 7 November.
His lawyer, Charles Cooper, told US media his client was not willing to appear voluntarily before the House committee members.
But Mr Cooper said he was ready to accept a subpoena – or legal summons to compel testimony – on Mr Bolton’s behalf.
The rush of possible new witnesses 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, and it is not guaranteed that those called will appear for depositions, even if they receive subpoenas as previous witnesses have.