Its software helps Ukraine target, for instance, tanks and artillery, a Palantir spokesperson said.
The company, whose co-founders include Karp and investor Peter Thiel, has opened an office in Ukraine.
"There are huge ethical issues on the battlefield," he said at an event Palantir hosted in Palo Alto.
Japan is a "very high priority" market for Palantir including in defense, another Palantir official, Kevin Kawasaki, said in an interview.
Reporting by Jeffrey Dastin in Palo Alto, Calif.; Editing by Stephen CoatesOur Standards: The Thomson Reuters Trust Principles.