Bradley Manning, the US soldier suspected of leaking a trove of secret military and diplomatic documents to the WikiLeaks website, is to be formally charged in a military court on Thursday.

The 24-year-old will be charged with 22 counts -- the most serious being aiding the enemy -- in a military hearing at a base north of Washington, DC. The judge will also set a date for the trial, expected in May.

The baby-faced soldier is accused of passing hundreds of thousands of military field reports from Iraq and Afghanistan and US diplomatic cables to WikiLeaks between November 2009 and May 2010, when he was serving in Iraq.

The leak of the military documents shed light on civilian deaths, while the diplomatic cables sparked a firestorm by disclosing the private remarks of heads of state and candid observations by senior US officials.

The US government slammed the disclosure of the documents by WikiLeaks, saying it threatened national security and the lives of foreigners working with the military and US embassies.

WikiLeaks supporters view the site as a whistleblower that exposed US wrongdoing and see Manning as a political prisoner.

Manning faces life in prison if convicted in the military court-martial. he is expected to plead not guilty.

Army investigators told last month's hearing that contact information for WikiLeaks founder Julian Assange, military reports, cables and other classified material had been found on computers and storage devices used by Manning.

Manning's defense attorneys have portrayed him as suffering during his deployment near Baghdad from emotional problems stemming from his homosexuality, which his superiors did nothing to remedy.

Jailed for more than a year and a half, Manning has complained of being placed in solitary confinement, of bullying by guards, and of being subjected to an overly restrictive regime at a US military prison near Washington.

The Bradley Manning Support Network said earlier this month that Manning had been nominated for the Nobel Peace Prize by members of the Icelandic parliament. It is not possible to verify who has been nominated for the awards.

Assange has meanwhile been in Britain fighting an extradition order from authorities in Sweden, where he faces rape and sexual assault accusations.

He has denied the allegations, saying they are politically motivated.