WASHINGTON — Amid a solemn silence, articles of impeachment against Donald Trump were read aloud on the Senate floor on Thursday as the bitterly divided chamber began a historic trial of the US president for abuse of power and obstruction of Congress.

Senate Sergeant of Arms Michael Stenger opened just the third impeachment trial of a US president in history with a warning to the 100 senators.

"Hear ye, hear ye, hear ye," Stenger said after the seven members of the House of Representatives who will serve as prosecutors gathered in the well of the Senate chamber.

"All persons are commanded to keep silent, on pain of imprisonment, while the House of Representatives is exhibiting to the Senate of the United States, articles of impeachment against Donald John Trump, President of the United States," the sergeant at arms said.

Adam Schiff, the chairman of the House Intelligence Committee who will serve as lead prosecutor for the trial, then read out the two articles of impeachment passed by the House on December 18.

"I will now read the articles of impeachment," Schiff said, "impeaching Donald John Trump, President of the United States, for high crimes and misdemeanors."

US Supreme Court Chief Justice John Roberts is to be sworn in at 2:00 p.m. (1900 GMT) to preside over the trial.

Roberts, 64, who was appointed to the nation's top court by president George W. Bush, will then deliver an oath to the 100 senators who will swear to administer "impartial justice."

The proceedings will then adjourn and the trial will get underway "in earnest" on Tuesday, according to Republican Senate leader Mitch McConnell.

Impeachment rules require a two-thirds Senate majority to convict and remove a president and Trump's acquittal is widely expected in the Republican-dominated Senate.

Trump is accused of abuse of power for withholding military aid to Ukraine and a White House meeting for the country's president in exchange for an investigation into his potential presidential election rival Democrat Joe Biden.

The Government Accountability Office concluded in a report released Thursday that the White House violated federal law by putting a hold on the congressionally-approved funds for Ukraine.

"Faithful execution of the law does not permit the President to substitute his own policy priorities for those that Congress has enacted into law," according to the GAO, a congressional watchdog.

The second article of impeachment — for obstruction of Congress — relates to Trump's refusal to provide witnesses and documents to House impeachment investigators in defiance of congressional subpoenas.

McConnell has been extremely critical of Trump's impeachment by the Democratic-controlled House and pledged on Thursday that things would be different in the Senate.

"It was a transparently partisan performance from beginning to end," McConnell said. "But it's not what this process will be going forward.

"This chamber exists precisely so that we can look past the daily drama," the Republican senator from Kentucky said. "The House's hour is over. The Senate's time is at hand."

The two articles of impeachment were delivered to the Senate on Wednesday in a solemn procession by the seven House Democrats who will prosecute the case against the 45th US president.

"So sad, so tragic for our country, that the actions taken by the president to undermine our national security, to violate his oath of office and to jeopardize the security of our elections, has taken us to this place," Democratic House Speaker Nancy Pelosi said as she signed the articles.

"This president will be held accountable," she said. "No one is above the law."

Pelosi held back on delivering the articles to the Senate as she pressured McConnell to agree to subpoena the witnesses and documents that the White House blocked from the House probe.

McConnell has refused to commit, saying the issue will only be decided after the trial's opening arguments and questioning.

A Trump administration official told reporters they expect the trial to last no longer than two weeks, suggesting McConnell could use his 53-47 Republican majority to stifle calls for witnesses and quickly take the charges to a vote.

Trump ridiculed the investigation and trial on Wednesday, as he has for months.

"Here we go again, another Con Job by the Do Nothing Democrats," he wrote on Twitter.

Democrats released documents this week that showed Trump's personal lawyer Rudy Giuliani worked with Ukrainian-born American Lev Parnas to pressure Kiev to investigate Biden.

They also showed the two, working with Ukrainian officials, trying to force out the US ambassador to the country, Marie Yovanovitch, eventually removed by Trump.

In a televised interview Wednesday, Parnas told MSNBC that "President Trump knew exactly what was going on."

"He was aware of all of my movements. I wouldn't do anything without the consent of Rudy Giuliani or the president," Parnas said.

Aside from Schiff the prosecution team will include Judiciary Committee chair Jerry Nadler; House Democratic Caucus chair Hakeem Jeffries; Zoe Lofgren, a veteran of two previous impeachment investigations; and three others. — AFP