WASHINGTON (AFP) - A US military judge ruled Friday (Nov 3) that Bowe Bergdahl, the US soldier who deserted his Afghanistan post only to be held captive by insurgents for five years, would serve no prison time after a politically charged trial.

The judge ordered Sergeant Bergdahl to be dishonorably discharged, his rank slashed to private, and that he pay a US$10,000 (S$14,000) fine, the Pentagon said.

During last year's presidential campaign Donald Trump said he believed Bergdahl should be put to death for abandoning his post in the war zone. Bergdahl had faced up to life in prison after pleading guilty to charges of desertion and endangering his fellow troops.

President Donald Trump on Friday blasted the judge's decision. "The decision on Sergeant Bergdahl is a complete and total disgrace to our Country and to our Military," Trump tweeted.

Earlier this week, Colonel Jeffery Nance, judge in the case tried in Ft. Bragg, North Carolina, warned that Trump's repeated comments on the case could "mitigate" the sentencing.

The case inflamed US political divisions over the Afghan war, with supporters calling Bergdahl a victim of the 16-year-old conflict and detractors labelling him a turncoat whose action led to severe injuries of fellow soldiers in his unit on search missions for him.

Prosecutors had demanded harsh punishment, calling on testimony from witnesses injured - including one soldier shot in the head and permanently disabled - while on search missions in eastern Afghanistan after Bergdahl disappeared in 2009.

But his defenders argued that he has already suffered from five years of brutal treatment by the Taliban and the related Haqqani group, before being released in a prisoner exchange for five Taliban fighters in 2014.