Washington, Nov 7: US President Donald Trump has lashed out at Democrats during a rally in Louisiana, as impeachment testimony from a senior US diplomat was released.

On Wednesday, Bill Taylor, the top US diplomat in Ukraine, testified that Trump officials threatened to withhold aid from Ukraine unless it agreed to investigate his Democrat presidential rival Joe Biden, the BBC reported.

Public impeachment hearings will begin on November 13, with Taylor set to be the first witness called.

Speaking at his rally in the city of Monroe on Wednesday night, Trump accused the Democrats of trying to overthrow American democracy via a "deranged, delusional, destructive and hyper-partisan" process.

The President accused the Democrats of "ripping the guts out of our country", suggesting they were engaged in an "illegal act".

He also attempted to discredit the whistleblower who flagged up his July 25 phone call with Ukrainian President Volodymyr Zelensky.

Trump said the whistleblower made a "horrible statement" about the call, which led to the impeachment probe.

Besides slamming the Democrats, Trump also sought to galvanise support for Republican businessman Eddie Rispone, who is bidding to unseat Democratic Governor John Bel Edwards in next month's state election.

The President told supporters Rispone will "defend your values", while accusing Edwards of being "dangerously soft on crime".

Meanwhile, the first public hearings of the inquiry will witness three State Department officials, including Taylor, testifying first, the BBC said.

So far, lawmakers from three key House of Representatives committees have heard from witnesses behind closed doors.

House Intelligence Committee chairman Adam Schiff, who is overseeing the inquiry, told reporters on Wednesday that an impeachment case was building against the President.

The Capitol Hill hearings will now be broadcast live, with both Democratic and Republican lawmakers questioning witnesses.

Impeachment is the first part - the charges - of a two-stage political process by which Congress can remove a President from office. If, following the hearings, the House of Representatives votes to pass articles of impeachment, the Senate is forced to hold a trial.

A Senate vote requires a two-thirds majority to convict and remove the President.

Only two US Presidents in history - Bill Clinton and Andrew Johnson - have been impeached, but neither was convicted. President Richard Nixon resigned before he could be impeached.

Trump lashes out at Democrats at Louisiana rally