India has stepped up efforts to sell an advanced cruise missile system to Vietnam and has at least 15 more markets in its sights, a push that experts say reflects concerns in New Delhi about China's growing military assertiveness.

Selling the supersonic BrahMos missile, made by an Indo-Russian joint venture, would mark a shift for the world's biggest arms importer as India seeks to send weapons the other way in order to shore up partners' defenses and boost revenues.

The government of Prime Minister Narendra Modi has ordered BrahMos Aerospace, which produces the missiles, to accelerate sales to a list of five countries topped by Vietnam, according to a previously unreported government note.