The US soldier held by insurgents for five years after disappearing from his post in Afghanistan has been charged with desertion and "misbehaviour before the enemy".

Sergeant Bowe Bergdahl, 28, was released in May last year in a controversial swap for five Taliban detainees held at the US-run prison at Guantanamo Bay, Cuba.

He could now face a life sentence in a US jail.

The only American in uniform to be held by insurgents in the Afghanistan war, Bergdahl was held captive by Taliban-linked Haqqani militants after he went missing from his base near the Pakistani border in June 2009.

Under the military's code of justice, Bergdahl faces one count of desertion "with intent to shirk important or hazardous duty" and one count of misbehaviour that endangers a command, unit or place, Colonel Daniel King told reporters at Fort Bragg, North Carolina.

Some desertion crimes carry a potential death sentence but authorities say the particular charge outlined against Bergdahl carries a maximum five years, as well as dishonourable discharge, reduction in rank and forfeiture of pay.

The count of "misbehaviour before the enemy" carries a potential life prison sentence.

The soldier's case will now be subject to a preliminary hearing, in which military authorities will decide if there is sufficient evidence for a trial.

Some soldiers who served at the same base have alleged Bergdahl walked out of his unit willingly, putting other troops at risk as they searched for him.

President Barack Obama's administration has defended the handling of the case, saying the government has an obligation to bring all US soldiers home and that military authorities will decide if Bergdahl violated his orders or duties.