The bitter feud between India's billionaire Ambani brothers, which bankers and analysts say is tarnishing the corporate image of India, has escalated further.

Anil Ambani has sent a furious letter to Reliance Industries, the conglomerate controlled by his elder brother, Mukesh, accusing it of "malafide interference" for its role in scuppering tie-up talks between his Reliance Communications and South Africa's MTN.