Bolivia, which lost former coastal territory during the War of the Pacific, argued earlier this week that Chile has not kept later diplomatic promises and obligations under international law to negotiate over “sovereign access” – presumably a land corridor and port under its control.

The issue has been a recurring area of contention between the Andean neighbors for decades.

Bolivia, which still retains a navy, wants a corridor to the sea to boost its exports of natural gas and minerals. Chile argues Bolivia already has access on favourable terms.

“The treaty is in effect and the border between Chile and Bolivia was agreed upon with clarity and in perpetuity. It’s time Bolivia stopped confusing its own aspirations with Chile’s obligations,” Chilean President Sebastián Piñera said after watching the arguments from Santiago.

Claudio Grossman, who spoke for Chile before the court, said the South American nation had already granted Bolivia more than what is required by the 1904 peace treaty.

“Bolivia benefits from access without restrictions to ports in Chile”, Grossman said.

Lawyers for Bolivia earlier this week said the country was not asking “the court to rule on how sovereign access should be arranged … but simply (to ensure) that Chile return to the negotiating table in good faith.”

Bolivian President Evo Morales said from La Paz on Thursday that Chile’s defense had made “much reference to the Treaty of 1904, suggesting that Chile complied perfectly with it.” But Chile had offered “no guarantee of free movement of people or goods,” he added.

Oral arguments run through March 28. Judges will then deliberate for several months before setting the date for a ruling.

The International Court of Justice is the United Nations’ highest court for disputes between nations. Its rulings are binding and cannot be appealed, though countries have occasionally flouted them.