Santiago Maldonado: Body found in search for Argentine activist
Santiago Maldonado, 28, was last seen in August during a confrontation between police and indigenous rights activists at a protest in Patagonia.
Mr Maldonado's disappearance caused a national outcry and has since become highly politicised.
The news comes ahead of Argentina's congressional elections on Sunday.
Both governing and opposition parties have suspended campaigning as the body is transported to Buenos Aires for identification.
Forensic experts have been assigned and an autopsy will take place at the request of the Maldonado family.
Prosecutor Silvia Avila said the body, discovered in a riverbed just a few hundred metres from where Mr Maldonado was last seen, was found with clothing that resembled those belonging to the missing activist, AFP news agency reports.
In a statement, the Maldonado family said that the true identity of the body and cause of death would not be known until "experts have completed their work".
They added: "We are asking that our privacy be respected at this difficult time."
Witnesses say Mr Maldonado was last seen after he was arrested at a demonstration for the rights of the Mapuche indigenous group in southern Argentina on 1 August.
On the day that he disappeared, border police clashed with protesters while dismantling a roadblock that had been erected on Route 40, the main road crossing Argentina from north to south.
Police later denied detaining Mr Maldonado.
Human rights campaigners, union leaders and left-wing groups had called on the government of Mauricio Macri, which has denied allegations of a cover-up, to do more to find him.
President Macri's government then offered a reward of almost $30,000 (£23,000) for information on his disappearance.
Meanwhile Mr Maldonado's brother, Sergio, has called for an independent investigation outside police authority.
In September, thousands of Argentines marched in the capital Buenos Aires to protest the activist's disappearance.
The rally was one of many protests in cities across Argentina.