NEW DELHI—Increasing numbers of drone sightings on the disputed India–Pakistan border have created fresh security warnings for India and have threatened the cease-fire between the two neighbors that’s been in place since late February. Experts said the militarization of drone technology is a part of new asymmetric means of warfare that is increasingly being used by nonstate actors around the world to attack civilian and military installations. Drones, or unmanned aerial systems (UAS), are very cheap to manufacture or acquire, compared to other air-to-surface military technology. They can overwhelm expensive defense systems and threaten a nation’s security. Seven drones were sighted on the disputed border inside India since the beginning of this month, while a “Pakistani quadcopter” was spotted inside Indian territory in the Arnia sector, 379 miles from the national capital, New Delhi, and was shot down by India’s Border Security Forces, according to Indian reports. More than 300 drones …