At least 100 pilots from India's debt-laden national carrier Air India failed to turn up to work on Tuesday in a move the civil aviation minister described as an "illegal" strike.

The airline, which loses nearly $2 million a day, is facing mounting problems due to rising fuel prices, competition from low-cost rivals and a record of labour disputes.

"About 100 pilots representing the Indian Pilots' Guild reported sick Monday night, leading us to cancel four international flights," K. Swaminathan, a spokesman for Air India, told AFP.

Swaminathan said the pilots were protesting against former Indian Airlines flyers -- who moved to Air India when the two firms merged -- also being trained for new Boeing 787 Dreamliner aeroplanes, claiming that would threaten their own career prospects.

"They have not given any notice for any strike," civil aviation minister Ajit Singh told reporters. "(The) strike is illegal."

The Indian government approved a restructuring plan last month to help turn around the fortunes of the beleaguered carrier, but warned that its performance would be strictly monitored.

Jitendra Awhad, chief of the Indian Pilots' Guild, told the CNN-IBN news channel that the pilots "had no other alternative left" but to stop work.

"I am asking for the aviation minister to intervene immediately. We know the difficulties the passengers are going to face but then it's for the management also to take a step forward," he said.

[An Air India passenger plane is parked at Chattrapati Shivaji International airport in Mumbai. AFP Photo]