KIEV, Feb. 21 - Prosecutors in Ukraine are investigating whether a member of Parliament committed treason by working with two associates of President Trump’s to promote a plan for settling Ukraine’s conflicts with Russia.

In a court filing on Tuesday, prosecutors accused the lawmaker, Andrii V. Artemenko, of conspiring with Russia to commit “subversive acts against Ukraine,” in particular by advancing a proposal that could “legitimize the temporary occupation” of the Crimean peninsula. Russia forcibly annexed the peninsula in 2014, a step that Ukraine, the United States and other governments have refused to recognize; Artemenko said his proposal would allow Ukraine to formally cede control of the territory to Russia, at least temporarily, the New York Times reported.