A bill under debate in the Peruvian Congress has increased diplomatic tensions with Chile.
Chile and Peru have a history of border disputes
The parliament in Peru has sped up the passage of legislation aimed at redrawing the sea border between the two Latin American neighbours.
If approved, the bill would assert Peruvian control over valuable fishing grounds.
Chile argues that the legislation violates territorial treaties signed in the 1950s.
It has launched a diplomatic campaign against the bill, saying that it wants an amicable solution to the dispute.
The Peruvian legislation was passed by a second important committee and could get final approval as soon as Thursday.
Peru and Chile have a history of border disputes dating back to the 19th century.
Chile fought the War of the Pacific against Peru and Bolivia from 1879 to 1883, winning Bolivia's outlet to the sea and extensive areas from Peru.
In recent months, relations have deteriorated over allegations that Chile supplied arms to Ecuador during a 1995 war with Peru - claims that the Chilean government has denied.
In May, Peru suspended free trade talks and confidence-building measures with Chile.
Peru also refused to support Chile to lead the Organisation of American States.