Donald Trump Impeachment To Go Ahead

US House Speaker Nancy Pelosi said she has instructed the House Judiciary panel to draft articles of impeachment against President Donald Trump over his effort to pressure Ukraine to investigate a political rival.

Pelosi delivered the historic announcement on Thursday as Democrats push toward a vote to impeach Trump, possibly by Christmas.

She said she was authorising the drafting of articles of impeachment "sadly but with confidence and humility.

"The President's actions have seriously violate the Constitution," Pelosi said.

Pelosi made the remarks a day after the Judiciary Committee held a hearing in which three constitutional law experts called by Democratic lawmakers said Trump had engaged in conduct that represents impeachable offenses under the Constitution.

Speaker of the House Nancy Pelosi announced an impeachment inquiry against President Trump earlier this year. Image: Getty

A fourth expert called by Republican lawmakers called the Democratic-led impeachment inquiry rushed and flawed.

The House Intelligence Committee this week submitted findings from its inquiry into Trump's push for Kiev to launch an investigation related to former US Vice President Joe Biden, a top contender for the 2020 Democratic presidential nomination.

Trump also wanted Ukraine to look into the discredited theory that Ukraine, not Russia, meddled in the 2016 US election.

Democrats have accused Trump of abusing his power by withholding $US391 million ($A573 million) in security aid to Ukraine - a US ally facing Russian aggression - to pressure Ukrainian President Volodymyr Zelenskiy to announce the investigation.

Donald Trump denies any wrong doing. Image: Reuters.

Trump has denied any wrongdoing and called the impeachment investigation a hoax.

After Pelosi delivered her statement on Thursday, Trump accused Democrats of trying to impeach him over "two totally appropriate (perfect) phone calls with the Ukrainian President".

"The Do Nothing, Radical Left Democrats have just announced that they are going to seek to Impeach me over NOTHING," Trump tweeted.

"They already gave up on the ridiculous Mueller "stuff," so now they hang their hats on two totally appropriate (perfect) phone calls with the Ukrainian President....

"This will mean that the beyond important and seldom used act of Impeachment will be used routinely to attack future Presidents. That is not what our Founders had in mind."

Trump had earlier tweeted before Pelosi's remarks: "If you are going to impeach me, do it now, fast, so we can have a fair trial in the Senate, and so that our country can get back to business."

White House press secretary Stephanie Grisham said immediately after Pelosi's announcement that the Democrats "should be ashamed".

The US House Judiciary Committee later announced it is to hold a hearing on Monday to receive presentations on evidence in the impeachment inquiry.

Counsels representing both Democrats and Republicans from the Intelligence and Judiciary committees will make the presentations, Representative Jerrold Nadler, the Democrat who heads the Judiciary Committee, said.