China has pledged to buy almost $80 billion of additional manufactured goods from the United States over the next two years as part of a trade war truce, according to a source, a target that could provide a much-needed boost for plane-maker Boeing but is being questioned by U.S. trade experts.

Under the trade deal to be signed on Wednesday in Washington, China would also buy over $50 billion more in energy supplies, and boost purchases of U.S. services by about $35 billion over the same two-year period, the source told Reuters late on Monday.

The "Phase 1" agreement calls for Chinese purchases of U.S. agricultural goods to increase by some $32 billion over two years, or roughly $16 billion a year, said the source, who was briefed on the deal.