Nicolas Maduro’s Venezuela and the Caribbean Community nation of Guyana are on the diplomatic warpath again in the wake of last month’s ruling by the World Court that it has the right to hear their decades-old quarrel over boundary markers.

Upset that the Dutch-based Court of Justice (ICJ) had supported Guyana’s contention that it can hear the case and settle it, Venezuela’s government reacted angrily to the ruling by issuing decrees claiming sovereignty and exclusive sovereign rights in waters and the seabed adjacent to Guyana’s coast in the western Essequibo region that Venezuela has long claimed as its own.

Venezuela has, since the late 1940s, claimed that an 1899 international boundaries commission that had demarcated boundaries between the two had cheated it out of Guyana’s Essequibo region that represents two-thirds of the country’s land mass. Guyana is as large as Britain or Idaho in the U.S.

The waters off the Essequibo are believed to contain billions of barrels of oil and large quantities of gas that Venezuela has admittedly coveted. American supermajor ExxonMobil has already done seismic work off that coast and has also successfully drilled two test wells in the area, indicating that it is a hydrocarbon minefield just waiting to be explored.

In the past week, Venezuela’s national assembly established a special committee to defend the Essequibo region. Authorities there also announced that they had unreservedly rejected the ICJ’s ruling.

“It is ours. It belongs to the Venezuelans and we are going to reconquer it in peace, in national union, we are going to achieve it,” Maduro told lawmakers, while reminding that Venezuela had not signed on as a party to the case and does not recognize such rulings.

For its part, President Irfaan Ali of Guyana denounced the latest diplomatic maneuverings by Caracas, noting that “it is deeply disturbing that, on Jan. 7th, the president of Venezuela, Mr. Nicolas Maduro, issued a decree claiming for Venezuela sovereignty and exclusive sovereign rights in the waters and seabed adjacent to Guyana’s coast, west of the Essequibo River. I remind that sovereignty over this coast, and the land territory to which it is attached, were awarded to Guyana (then British Guiana) in the 1899 Arbitral Award, whose validity and legally binding character Guyana is confident the International Court of Justice (ICJ) will uphold unequivocally. Therefore, this attempt by Venezuela to attempt, unilaterally, to fix both its land and maritime boundaries with Guyana is a legal nullity, which cannot, and will not, be respected by any other state in the world, including Guyana.”

Guyana wants a quick settlement to the case as perennial diplomatic flare ups and periodic acts of military aggression by Venezuela have only served to chase away international investors and allow tensions to simmer.

In 2013, Venezuelan gunboats had arrested and expelled a seismic rig working for a Texas offshore concession awardee and kept the crew in detention for about a week. Two years ago this month, a Venezuelan helicopter tried to land on an exploratory vessel leased by Exxon Guyana, again raising tensions. This is a major reason Guyana wants a hurried ruling on the boundary demarcation issue.

Meanwhile, the U.S. government has thrown its support behind Guyana in the dispute.

Acting assistant secretary for U.S. Department of State’s Bureau of Western Hemisphere Affairs, Michael Kozak late Sunday, Jan. 10 tweeted that the U.S. supports the ICJ’s ruling, suggesting that “is the legal and peaceful way forward. Maduro’s aggressive claims don’t change this. They only show the world his disregard for his neighbors and international law.”

Maduro has in recent weeks been suggesting that direct talks with Guyana should be the way to go. Guyana has countered that decades of U.N.-mediated direct talks have produced nothing of substance so the best route for a once and for all settlement is a World Court ruling.