Russia investigation: What is a US grand jury and how does it work?

Unlike a typical trial, grand jury proceedings are not public

The use of a grand jury, a standard prosecution tool in criminal investigations, suggests that Mueller and his team of investigators is likely to hear from witnesses and demand documents in the coming weeks (AP)

The special counsel investigating claims of Russian meddling in the US election has assembled a grand jury - but what does this mean?

In May Robert Mueller, a former director of the FBI, was assigned to investigate if there were links or co-ordination between Donald Trump's campaign and the Russian government during his election campaign.

Since then he has been gathering information and considering whether there is evidence of collusion - and if so whether it warrants criminal charges.

On Thursday reports emerged that Mr Mueller had appointed a "grand jury", leading to speculation that his investigation has intensified.

In the US justice system a prosecutor studies the information gathered as part of an investigation before deciding whether to present the evidence to a grand jury.

A grand jury is typically made up of between 16 and 23 laypeople - members of public - selected in a similar manner to a jury in a criminal trial in England and Wales.

The impartial body is given an outline of the case against an individual or individuals by the prosecutor, who will show them any evidence or call witnesses to testify under oath before them.

All proceedings before a grand jury are "sealed", meaning only the people in the room have knowledge of what has been discussed.

After listening to the prosecutor and any witnesses the grand jury retires to vote in secret on whether enough evidence exists to charge a person with a crime.

The grand jury process is a constitutional requirement in the US for some offences.

What the empanelling of a grand jury in the Russia probe means for Mr Trump's administration is yet to emerge.

Making his first public appearance after the news broke, the President told a rally of supporters in West Virginia: "I just hope the final determination is a truly honest one."

PA