Brazil “has intensified defensive actions” along its northern border as it monitors a territorial dispute between its neighbors, Guyana and Venezuela, the country’s defense ministry said on Wednesday.

“The Ministry of Defense has been monitoring the situation. Defensive actions have been intensified in the northern border region of the country, promoting a greater military presence,” it said in a statement.

Brazil’s push to move more military resources north comes amid rising tensions between Venezuela and Guayana over an oil-rich region known as the “Esequiba,” which constitutes over two thirds of Guyana’s total land mass.

Venezuela’s claims on the Esequiba, which have been the source of a long-running territorial dispute, were reignited in recent years after Guyana’s discovery of oil and gas near the maritime border. The 160,000 square km (61,776 square mile) territory is mostly impenetrable jungle.

On December 3, Venezuelans will vote in a referendum on “the rights” to the Esequiba. The International Court of Justice (ICJ) is expected to rule on Friday on a request by Guyana that the referendum be called off. Venezuela’s government has said it will go ahead no matter what.

The referendum asks Venezuelans among other things if they agree with Caracas’ position to reject the ICJ’s jurisdiction over the Esequiba region and agree to a plan to incorporate it and create a state called Guayana Esequiba. It would also grant its population Venezuelan citizenship.

In April the International Court of Justice ruled that it had jurisdiction over the border issue. But a final ruling on the main case could be years away.

Venezuela protested an oil tender announced by Guyana in September, arguing that the offshore areas are subject to dispute and the companies awarded the fields will not have the rights to explore them.

The referendum has been described by critics as a way for the ruling party to test its support ahead of planned elections next year and to encourage the international courts to give it full rights over the disputed border territory.

The Venezuelan communications ministry did not immediately respond to a request for comment on Brazil’s actions.

-Reuters