Peruvian lawmakers are set to vote as early as Thursday on a measure that would set maritime boundaries with Chile without Chilean consent.
Chilean President Ricardo Lagos has formally objected to the move, saying Wednesday that Chile will continue to exercise full sovereignty over its maritime territory. Chile's lower house of congress voted Wednesday to support his position, which says the maritime border was set in a treaty 50 years ago.
Chilean government spokesman Osvaldo Puccio has been lobbying Brazil and Argentina for support on the issue, which concerns an area rich in marine life.
Peru claims the maritime border was never clearly defined.
Both countries have said they will reinforce their borders with military forces if necessary.