WASHINGTON — Then there was one.

Syria announced during United Nations climate talks on Tuesday that it would sign the Paris agreement on climate change. The move, which comes on the heels of Nicaragua signing the accord last month, will leave the United States as the only country that has rejected the global pact.

According to several people who were in a plenary session at the climate talks in Bonn, Germany, a Syrian delegate announced that the country was poised to send its ratification of the Paris agreement to the United Nations.

“This is the very last country that actually announced, so everyone has joined and the U.S. is now so isolated,” said Safa Al Jayoussi, executive director of IndyAct, an environmental organization based in Lebanon that works with Arab countries on climate change.