Bradley Manning, the US soldier accused of leaking classified information to whistleblowing website WikiLeaks, has been formally charged after declining to enter a plea in a military trial which could see him jailed for life.

Manning, a 24-year-old former intelligence analyst, was charged on Thursday with 22 counts, the most serious of which is "aiding the enemy," which carries a maxium sentence of life in prison. The other charges carry a combined maximum of 150 years behind bars.

Dressed in a US Army uniform and flanked by his lawyers, Manning was silent during the 45-minute arraignment, responding only "Yes, your honour," when asked by military judge Denise Lind whether he understood the charges against him.

Manning deferred entering a plea, which he is not required to do until the start of the court martial. He also declined to say whether he preferred to be tried before a single military judge or a military jury.

The former US private 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.

Defence lawyers say Manning was troubled and shouldn't have had access to classified material.

Manning, a native of Oklahoma, has been locked up since May 2010.

At a preliminary hearing in December, military prosecutors produced evidence that Manning downloaded and electronically transferred to WikiLeaks nearly half a million sensitive battlefield reports.

Prosecutors presented excerpts of online chats found on Manning's personal computer that allegedly document collaboration between him and WikiLeaks founder Julian Assange.

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.