Two others who tried to escape via the same route after clashes with irate demonstrators Sunday were still missing, and a search was under way.

Soldiers said they came under attack from people armed with slingshots and sticks at a demonstration against the government of President Dina Boluarte in the city of Ilave in the Puno region.

Puno has been the epicenter of demonstrations that first broke out in December when then-president Pedro Castillo was ousted and arrested after trying to dissolve parliament and rule by decree.

His supporters are demanding the resignation of Boluarte, fresh elections, a new constitution and the dissolution of parliament.

More than 50 people have died and over 1,300 were injured -- nearly half of them members of the security forces -- in clashes since then, according to the country's rights ombudsman.

The latest victims, the four soldiers, were identified by the defense ministry Monday as Franz Canazas, Alex Quispe Serrano, Elvis Pari and Elias Lupaca.

Their bodies were retrieved from the Ilave River, a tributary to Lake Titicaca on the border between Peru and Bolivia.

In a video distributed by the ministry, a soldier who managed to escape alive testified he and his colleagues "crossed the river... because we had no other way out."

"Between 800 and 900 people surrounded us and started throwing stones at us," he recounted. "People called us corrupt and murderers."

He said the men had tried to form a human chain, but "the current took us, and... some of the troops began to drown."

A healthcare group in Puno said on Sunday it had treated five soldiers for hypothermia after local residents rescued them from the river.

On Saturday, 16 people -- civilians and soldiers -- were injured in clashes elsewhere in Puno that also saw a police station burnt.

Castillo, 53, is serving 18 months of pre-trial detention in Lima, accused of rebellion. He was under investigation on several counts of corruption.

The demonstrations are driven by poor southern Indigenous Peruvians who perceive Castillo -- who is also from humble origins and has Indigenous roots -- as an ally in their fight against poverty, racism and inequality.