June 21 is being celebrated the world over as the International Day of Yoga. In India, the main event was kick-started by prime minister Narendra Modi who performed yoga along with over 50,000 enthusiasts at Dehradun's sprawling Forest Research Institute. Modi called yoga as the most powerful unifying force in a strife-torn world. People across the country celebrated the day with mass yoga performances. In Ladakh, Indo-Tibetan Border Police personnel performed the Surya Namaskar at an altitude of 18,000 feet while in Mumbai, Indian Navy personnel celebrated the day on board the INS Virat. Watch the HT video.