US trade officials on Monday said they will launch an investigation that could result in tariffs on solar panels imported from four Southeast Asian nations, a blow to clean energy project developers that rely on cheap imports to keep costs down.

The Commerce Department's decision regarding imports from Malaysia, Thailand, Vietnam and Cambodia was a victory for Auxin Solar. 

The San Jose, California-based solar manufacturer this year requested the probe, arguing that Chinese manufacturers shifted production to those nations to avoid paying US duties in place for...