The US former national security advisor was so alarmed by a White House–linked effort to pressure Ukraine to investigate Democrats, he told aide Fiona Hill to alert the National Security Council’s chief lawyer, Hill told House impeachment investigators in her 10-hour deposition on Monday.

Bolton also warned that President Donald Trump’s personal attorney Rudy Giuliani, who has emerged as the point man in the president’s alleged drive to pressure Ukraine to dig up dirt on Democratic presidential hopeful Joe Biden, is “a hand grenade who’s going to blow everyone up,” his aide Fiona Hill told lawmakers, New York Times reported.

The remark, which was also reported by NBC News, came after Trump’s former top Russia advisor Hill sat for an hours-long closed-door deposition before US lawmakers probing whether to impeach the president.

Referring to acting White House chief of staff Mick Mulvaney, Bolton also said that “I am not part of whatever drug deal Rudy and Mulvaney are cooking up,” the Times reported, citing two sources familiar with Hill’s deposition.

Her testimony came after allegations that Trump pushed Ukrainian President Volodymyr Zelensky to investigate the Bidens in a July 25 phone call, which sparked an impeachment inquiry by the House of Representatives.

On Saturday, Trump defended his personal attorney, Rudy Giuliani, who is reportedly under federal investigation over his dealings with Ukraine on the president’s behalf.

Taking to Twitter, Trump said, “So now they are after the legendary ‘crime buster’ and greatest Mayor in the history of NYC, Rudy Giuliani”.

Earlier this month, Ukraine’s former president had said that he discussed investments with President Donald Trump’s attorney, Rudy Giuliani, in 2017, but that he never discussed Ukrainian companies with any US official.

Giuliani, a former federal prosecutor and ex-mayor of New York City, has acknowledged that he and two associates worked with Ukrainian prosecutors to collect information on Biden, his son Hunter and the US ambassador to Ukraine Marie Yovanovitch, who was recalled in May.

On Monday evening, Giuliani said, “I don’t know Fiona and can’t figure out what she is talking about,” and that the State Department arranged all his contacts with Ukraine, according to The Washington Post.

Last week, the Times reported that Giuliani was himself under federal investigation for his dealings with Kiev on Trump’s behalf.

Earlier in September, President Trump fired Bolton, who is known for his hardline stances on Washington’s archenemies, particularly Iran, North Korea and Venezuela. He was replaced by Robert C O’Brien.