Trump administration accuses Democrats of intimidation

In a letter to Congress, US Secretary of State Mike Pompeo questioned whether the powers of the three parliamentary committees under investigation - the Foreign Affairs Committee, the Intelligence Committee, and the Oversight and Reform Commission - could summon diplomats to testify about President Donald Trump's quest for information detrimental to his political rival Joe Biden.

Pompeo said the five officials would not respond to the summons and the committees next week threatened to seek justice.

Pompeo also doubted that the powers of the committees would allow them to ask diplomats to hand over official documents on Ukraine.

He recalled that summoning these diplomats "can only be understood as an attempt to intimidate and offend outstanding professionals in the State Department."

He added, "I will not be tolerant with such tactics, and I will use all my means to prevent and expose every attempt to intimidate dedicated professionals who are proud of their leadership."

The Wall Street Journal reported on Tuesday that Pompeo was among those present when President Donald Trump made a phone call to his Ukrainian counterpart Vladimir Zelinsky on July 25, prompting Democratic lawmakers in Congress to kick him out of office.