Beijing sought to ease tensions with Washington as its top trade negotiator told U.S. officials that China was planning to reduce auto tariffs and boost purchases of soybeans and other crops, according to people in both capitals briefed on the discussions.

The two sides held a teleconference involving Treasury Secretary Steven Mnuchin, U.S. Trade Representative Robert Lighthizer and Chinese Vice Premier Liu He, the first session since the two sides had reached a 90-day trade truce on Dec. 1 in Buenos Aires. But it is unclear...