US President Donald Trump has demanded an immediate impeachment trial in the Senate, amid an impasse among Democrats and Republicans over when it may start.

The House impeached Trump on charges of abuse of power and obstruction of Congress.

But Democrats have yet to embark on the next stage, arguing the Republican-controlled Senate is refusing witnesses and will not hold a fair trial.

The Senate's numbers mean Trump is almost certain to be acquitted.

Now that the US House of Representatives has voted to impeach  Trump, the matter moves to the Senate for a trial which will be the third for an American President.

A two-thirds majority, basically 67 senators is required to convict and remove Trump.

Republicans control the Senate, 53-47, and Trump is widely expected to be acquitted.

Any senator could also propose a motion to dismiss the charges and a simple majority vote is needed for this.

Trump is only the third president to face a Senate trial for “high crimes and misdemeanors".

The first two, Andrew Johnson and Bill Clinton, were both acquitted.

Another president, Richard Nixon, resigned rather than face impeachment and trial.

[Source: BBC / New York Times]