India's aviation watchdog has deferred a June 1 deadline for airlines to adopt new rules on rest and duty times for pilots, a notice on its website showed, but without stating a reason or a new target date.

Tuesday's news followed a warning from a key airline lobby group, reported last month by the Economic Times newspaper, that the scramble to meet the new rules could force cancellation of up to a fifth of flights.

Announced in January, the rules increased flight crews' weekly rest periods to 48 hours from 36 and cut pilots' night flight duty times to a maximum of 10 hours from 13.

In this week's revised website notice, however, the Directorate General of Civil Aviation (DGCA) allowed airlines to retain the older norms for the time being.

The rule changes followed a review of data on pilot fatigue drawn from spot checks and airline surveillance after a pilot for budget carrier IndiGo collapsed and died in August before his flight.

The Federation of Indian Airlines warned of the cancellation risk as the watchdog's deadline left too little time to hire and train the 25% more pilots required to satisfy the new rules, Economic Times said.

Last week, Tata Group-owned Air India was fined 8 million rupees ($96,000) by the regulator, for breaching limits on flight duty times and fatigue management. ($1=83.3100 Indian rupees) (Reporting by Rama Venkat in Bengaluru; Editing by Clarence Fernandez)