NEW DELHI, June 18 (Reuters) - India's Prime Minister Narendra Modi told U.S. President Donald Trump late on Tuesday that a ceasefire between India and Pakistan after a four-day conflict in May was achieved through talks between the two militaries and not U.S. mediation, India's senior-most diplomat said. Trump had said last month that the nuclear-armed South Asian neighbours agreed to a ceasefire after talks mediated by the U.S., and that the hostilities ended after he urged the countries to focus on trade instead of war.