Tata employees have been sent a letter by the group's interim chairman.

Ratan Tata, of the Tata Sons conglomerate, reassured employees on the future of the group and its companies, in a letter seen by Reuters on Tuesday.

Tata reportedly said the decision to change the top management at Tata Sons was a difficult but well-deliberated one taken for the future success of the group, and to maintain the Tata culture and value system.

The letter, sent to employees on Tuesday, came a week after Tata sacked chairman Cyrus Mistry. He and the Tata group have traded barbs in public on a near daily since then, Reuters noted.

In an unusual, open letter to the board, he expressed his shock at the 'invalidity and illegality' of the move and said the board 'has not covered itself in glory'.

He also described a 'challenging situation' at Tata Motors due to its credit arm offering 'extended credit with lax risk assessment'.