U.S. President Barack Obama and Indian Prime Minister Narendra Modi have welcomed the start of preparatory work on six nuclear reactors in India, a key step in closing the first deal stemming from a U.S.-India civil nuclear accord struck over a decade ago.The two leaders said in a joint statement that India and the U.S. Export-Import Bank intend to work together toward a competitive financing package for the project and will work to finalize contractual agreements by June 2017.