Peruvian police have clashed with nationalist activists who planned to protest a decades-old agreement defining the country's maritime border with Chile.

At least 500 protesters left the Peru's southern city of Tacna for the Chilean border Wednesday, but were stopped by police during a routine security check on the Panamerican highway.

Activists then threw stones at the police, who responded with tear gas.

Former Peruvian presidential candidate Ollanta Humala called the demonstration to pressure the Peruvian government to do more to regain territory lost to Chile in a war in 1883.

Peru's cabinet chief, Jorge del Castillo, criticized the protesters for trying to damage relations with Chile.

Chile says its maritime border with Peru was defined in treaties 50 years ago. Peru passed a law last year that says the sea boundary is still undefined.

Some information for this report was provided by AFP, AP and Reuters.