House Speaker Nancy Pelosi on Tuesday announced the launching of formal impeachment proceedings against US President Donald Trump.

"Today, I'm announcing the House of Representatives is moving forward with an official impeachment inquiry. I'm directing our six committees to proceed with their investigations under that umbrella,” she said in a press conference.

“For the past several months we have been investigating in our committees and litigating in the courts so the House can gather all the relevant facts and consider whether to exercise its full Article 1 power, including a constitutional power of the utmost gravity, approval of articles of impeachment,” Pelosi said.

“Our republic endures because of the wisdom of our constitution enshrined in three coequal branches that act as checks and balances,” Pelosi added. “The president must be held accountable. No one is above the law.”

Trump wrote on Twitter in response, “Such an important day at the United Nations, so much work and so much success, and the Democrats purposely had to ruin and demean it with more breaking news Witch Hunt garbage. So bad for our Country!”

“They never even saw the transcript of the call. A total Witch Hunt! PRESIDENTIAL HARASSMENT!” he added.

Sources in the Democratic party reported earlier that Pelosi’s announcement would be made following a meeting with all Democratic members of the House of Representatives over allegations that President Trump threatened to withhold aid to Ukraine unless its government investigated actions by former US Vice President Joe Biden.

Biden is currently the frontrunner for the Democratic nomination to challenge Trump in the 2020 presidential election.

165 Democratic members of Congress have come out in favor of impeachment proceedings against Trump, more than two thirds of the Democratic caucus amid whistleblower reports of a phone conversation between Trump and Ukrainian President Volodymyr Zelensky.

President Trump condemned calls to impeach him, calling them a "witch hunt" as he called previous investigations and accusations against himself and his administration. The president has also stated that an unredacted version of his conversation with Zelensky.

Pelosi had previously been reluctant to pursue impeachment against Trump despite pressure from within her party.