BUENOS AIRES—China and the U.S. agreed to a cease-fire in a trade battle that has shaken global markets, with the U.S. postponing plans to increase tariffs on $200 billion in Chinese goods and the two sides entering negotiations on other contentious issues.

The truce was designed to ease tensions after months of escalating trade conflict, and held out the prospect that the world’s two largest economies could find an accommodation that would set their trading relationship on a different path. Amid the consensus, though, there...