Washington (CNN) Secretary of State Mike Pompeo refused to counter a discredited conspiracy theory that Ukraine interfered in the 2016 presidential election and sidestepped a question about his willingness to testify before the House impeachment inquiry.

President Donald Trump tweeted Tuesday morning that he would "love to have Mike Pompeo, Rick Perry, Mick Mulvaney and many others testify about the phony Impeachment Hoax."

Asked about the tweet during a briefing with reporters at the State Department, Pompeo said "when the time is right all good things happen."

The top US diplomat was briefing on a range of issues, from Cuba to Afghanistan and Iran, but was also questioned on the impeachment inquiry and Ukraine.

When asked if he believes the US and Ukraine should investigate whether Ukraine interfered in the 2016 election -- a theory that US intelligence agencies say has been spread by Russia in an effort to deflect blame -- Pompeo said it was the government's "right" and "duty" to do so in every instance.

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