The world’s leading oil exporter has become the most forceful opponent of a new agreement at the U.N. climate summit, according to people inside the talks.

The Saudi delegation has flatly opposed any language in a deal that would even mention fossil fuels — the oil, gas and coal that, when burned, create emissions that are dangerously heating the planet. Saudi negotiators have also objected to a provision, endorsed by at least 118 countries, aimed at tripling global renewable energy capacity by 2030.