RIO DE JANEIRO, Brazil, (AFP) — Brazilian President Luiz Inacio Lula da Silva voiced “growing concern” Thursday over a deepening border dispute between neighbouring Guyana and Venezuela, warning against a war in South America.

“If there’s one thing we don’t want here in South America it’s war,” the veteran leader told a summit of the Mercosur regional bloc in Rio de Janeiro as tensions surge over Essequibo, an oil-rich region under Guyanese administration but claimed by Venezuela.

“We have been following the development of the Essequibo issue with growing concern,” Lula said, calling on the Community of Latin American and Caribbean States to approach both sides about holding negotiations and saying Brazil stood ready to help.

“We don’t need conflict. We need to build peace,” he said.

South American giant Brazil, which borders both Guyana and Venezuela, has been monitoring the dispute.

The Brazilian army said Wednesday it was reinforcing its presence in its northern border region.

Tension over Essequibo has soared since President Nicolas Maduro’s government held a controversial referendum Sunday in which 95 percent of voters supported declaring Venezuela the region’s rightful owner, according to official results.

On Tuesday, Caracas proposed a bill to create a Venezuelan province in Essequibo, and ordered the state oil company to issue licenses for extracting crude in the region.

Guyana has administered Essequibo, which makes up more than two-thirds of its territory, for more than a century. But Venezuela has claimed it for decades.

The row intensified after ExxonMobil discovered oil in Essequibo in 2015, helping give Guyana — population 800,000 — the world’s biggest crude reserves per capita.