"This accident during relief operations has come as a huge shock to me. My heart goes out to the families of those who have lost their lives. The nation mourns with me the loss of our heroes whose selfless work has saved thousands of lives," Singh said.
"Our forces are conducting a heroic task in rescue and relief work in Uttarakhand. Continuing their work would be the best homage to them," he added.
Twentypeople, including Air Force and para-military personnel, were feared killed when an IAF helicopter crashed near Gaurikund in Uttarakhand during rescue operations. Among the dead were three IAF officers, an Air Force spokesperson said.