US House Speaker Nancy Pelosi says President Donald Trump's actions in the impeachment inquiry amount to "bribery".

Pelosi told reporters on Thursday that while Trump says his call with Ukraine was "perfect", she thinks "it's perfectly wrong".

Bribery is an impeachable offence spelled out in the US constitution.

The House opened public hearings this week in the impeachment inquiry. It revolves around Trump asking the Ukraine president for a "favour" in a July phone call. Trump wanted an investigation of Democrats and 2020 rival Joe Biden, while withholding military aid, according to the testimony.

Trump calls the inquiry a "hoax" and a "sham".