Landlocked Bolivia took its neighbour Chile to court on Monday, seeking to resolve a century-old dispute over precious access to the Pacific Ocean which has bedevilled bilateral ties.
La Paz is urging Santiago to return to talks, contending it has "an obligation to negotiate with Bolivia in order to reach an agreement granting Bolivia a fully sovereign access to the Pacific Ocean."
In a sign of the country's determination, Bolivian President Evo Morales is heading up the Bolivian delegation to the UN's highest court, the International Court of Justice (ICJ), based in The Hague.
"We have history, justice and right on our side," Morales said in a Tweet as seven days of hearings into the case opened in The Hague.
Bolivia, South America's poorest country, became landlocked after losing a four-year war against Chile in 1883, forfeiting territory and its access to the sea.
Following some 130 years of fruitless negotiations with Santiago, La Paz lodged a complaint with the ICJ in April 2013.
"We have waited a long time for this opportunity, but we are a patient and determined people," said former Bolivian president Eduardo Rodriguez Veltze, addressing the court.
Chile had made "a repeated and consistent commitment to Bolivia to end its landlocked situation," he maintained, saying the lack of sea access had had a devastating effect on the impoverished country's development.
"By fulfilling this promise to its neighbour, two countries united by culture, geography, history and fraternal spirit can heal all wounds and move forward," Veltze added.
The "entire Bolivian nation" was tuning into the proceedings in The Hague via giant screens erected in their cities, he said.
"We are here with one voice in pursuit of justice," he said, explaining the country once had 400 kilometres (248 miles) of coastline in the Atacama desert.
"Today it has none," he said.
According to estimates, Bolivia's "annual GDP growth would be at least 20 percent higher" if it had not been stripped of a sea access.
- 'An old debt' -
While its transport costs are estimated to be 31 percent higher than the continental average, he said.
"More than a century has passed since the Chilean invasion of Bolivia's coast... an act of aggression that resulted in territorial dismemberment and the painful loss of sovereign access to the sea."
Allowing access "would make a small difference to Chile, but it would transform the destiny of Bolivia," Veltze said.
About two dozen Bolivian activists have also arrived in The Hague from around Europe to support La Paz.
"This is an old debt that needs to be settled," Amancay Colque told AFP, as they held up a large flag outside the Peace Palace.
The loss of the Chuquicamata mine, the world's largest open-pit copper mine which is situated in the disputed area, had badly hit the country’s indigenous peoples, Colque said.
"This is about justice, we want this to be addressed. We want Chile to fulfil its promises, and we want it done in a peaceful way," she added.