"We have had a significant number of flight cancellations and delays in the past few days due to various reasons including crew unavailability," a company spokesperson said in a statement.

Vistara, owned by Tata Group and Singapore Airlines, is using larger aircraft, including the wide-body Boeing 787 Dreamliner on certain domestic routes "to accommodate more passengers, wherever possible," the spokesperson said.

The airline, which will be merged with Tata-owned Air India, faced similar disruptions last month.

Local media had reported that an increasing number of its pilots had called in sick. In response, Vistara had said the disruption was not attributed to pilot absenteeism alone as it also had to deal with certain unforeseen maintenance needs.

Vistara's flight disruption comes as India's aviation watchdog deferred a June 1 deadline for airlines to adopt new rules on rest and duty times for pilots, a move that has drawn criticism from some pilots and aviation safety experts.

(Reporting by Nandan Mandayam in Bengaluru; Editing by Anil D'Silva)