Landlocked Bolivia sued neighboring Chile in the Hague on Wednesday as it pressed a longstanding claim to recover land lost in a 19th century war and thus regain access to the Pacific.
Chile quickly responded that the issue was not negotiable.
In filings to the International Court of Justice, Bolivian Foreign Minister David Choquehuanca said the suit "assumes the historical mandate of the Bolivian people" to revert to being a maritime nation.
Bolivia has been preparing its legal, historical and economic arguments for the lawsuit for more than two years.
In a war fought with Chile in 1879, Bolivia lost nearly 400 kilometers (250 miles) of coastline and 120,000 square kilometers of land.
For years, Bolivia has been pressing Chile to grant it a useful and sovereign outlet to the sea.
Chile, Bolivia's neighbor to the southeast, has refused.
It says a peace and friendship treaty signed by the two countries in 1904 established their common borders.
Choquehuanca, speaking from the Hague, said the suit demands that Chile negotiate in good faith with Bolivia "a swift and effective agreement that grants it fully sovereign access to the Pacific Ocean."
Chile's President Sebastian Pinera vowed to use "all" instruments within its reach in treaties and international law.
"We are going to defend with all the force in the world every square meter of our territory and every suqare meter of our (territorial) sea," he added.
Chilean Interior Minister Andres Chadwick later told reporters that "Chile knows full well that we can talk, we can have a dialogue, we can discuss best practices between neighbors.
"But if they are trying to talk about maritime sovereignty, which is what they are after, no: there is going to be no dialogue."
Bolivia says the 1904 agreement is not valid because it was signed under pressure from Chile.
The two countries have tried for years but failed to reach agreement on their territorial dispute.
In 2006, Bolivian President Evo Morales opened up a channel of direct dialogue with his then Chilean counterpart Michelle Bachelet, but it led nowhere.