Former National Security Adviser John Bolton was so concerned about Rudy Giuilani‘s attempt to enlist help from Ukraine that he instructed an aide to warn White House lawyers about the effort, it was reported Monday, warning that the former mayor is “hand grenade.”

According to The New York Times, Bolton had a heated conversation over the summer with Ambassador to the European Union Gordon Sondland, who along with Giuliani and President Donald Trump was coordinating a scheme to solicit help from Ukraine’s government to investigate Joe BidenThe discussion between Bolton and Sondland reportedly came two weeks before Trump’s infamous call to Ukrainian President Volodymyr Zelensky, in which the former pressured the latter to probe the 2020 Democratic candidate.

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Bolton aide Fiona Hill said in her closed-door testimony on Monday that the former George W. Bush administration official directed her to alert John Eisenberg, the top attorney for the National Security Council, about the involvement of Sondland, Giuliani and acting White House Chief of Staff Mick Mulvaney in the Ukraine controversy.  Hill said Bolton told her he wanted no involvement in the “drug deal” Mulvaney and Sondland were preparing regarding Ukraine. The State Department tried to stop Sondland from testifying before lawmakers about his role in the scandal.

“I am not part of whatever drug deal Sondland and Mulvaney are cooking up,” Bolton told Hill to say to White House attorneys. The Times also reported that Hill said Bolton told her he believed Giuliani was “a hand grenade who’s going to blow everybody up.”

Hill, the senior director for European and Russian affairs, also reportedly challenged Sondland directly by citing the fact that dealing with Ukraine was not part of his responsibilities, as the country is not a member of the European Union. However, Sondland responded by insisting that Ukraine was part of his duties.