India, Feb. 7 -- The United States is in the process of sending back close to 600 more illegal migrants to India, even as Indian authorities on Friday said that New Delhi has conveyed its concerns to Washington at the treatment of deportees after images of people in shackles repatriated on a military flight triggered a nationwide outcry.

While the US informed the Indian side some time ago that 487 "presumed Indian citizens" were served with final removal orders, another 203 illegal migrants were rounded up in sweeps by American authorities, mostly along the border with Mexico, last month, people familiar with the matter said on condition of anonymity.

Of the 203 detained recently, 104 were sent back on a C-17 military aircraft that land...