Sonia condoles Nepalese leader Sushil Koirala's death
She said he led his country during extremely difficult and testing times and contributed immensely to its transition into a republic.
His contribution to fostering Indi-Nepal ties will always be remembered, she said in a statement.
Koirala, who was credited with promulgating the country's new Constitution in September last year to complete a stalled peace process, died today after a bout of pneumonia.
79-year-old Koirala had served as Nepal's Prime Minister from February 2014 to October 2015 and was the president of Nepali Congress, the country's biggest political party.