"Saddened at the passing away of former Prime Minister of Nepal, Sushil Koirala. My condolences to his fellow citizens, family and friends," Banerjee 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.