Landlocked Bolivia sued neighboring Chile Wednesday in the Hague as it pressed a longstanding claim to recover land lost in a 19th century war and thus regain access to the sea.
Chile quickly responded that the issue was not negotiable.
Bolivian Foreign Minister David Choquehuanca filed papers at the International Court of Justice, saying 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 (46,300 square miles) 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."
Chilean Interior Minister Andres Chadwick later told reporters that "if they want to talk about Chile's maritime sovereignty, no. No dialogue is possible."
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 President Evo Morales opened up a channel of direct dialogue with his then Chilean counterpart Michelle Bachelet, but it led nowhere.