Mumbai: Cyrus Mistry and Ratan Tata have ratcheted up their war of words. The office of Mistry, the ousted Tata Group chairman, fired off another letter claiming that Ratan Tata and Tata trustee N.A. Soonawala had been closely consulted when the group finalised the strategy on its legal slugfest with NTT Docomo. The Japanese telecom company has been frustrated in its attempts to sell its 26.5 per cent stake in Tata Teleservices at a pre-determined price set out in a shareholders' agreement signed in 2009.

"Insinuations that the Docomo issue was handled under the watch of Mr Mistry in a manner inconsistent with Tata culture and values are baseless," said the latest note issued from Mistry's office.

While justifying the move to oust Mistry, Tata Sons had said: "The tenure of the former chairman was marked by repeated departures from the culture and ethos of the group."

Later, sources close to the group released a letter that Ratan Tata had sent out to employees in which he said Mistry's removal was "absolutely necessary" for the future success of the Tata group.

The Docomo issue has been festering for a long time. The Japanese company had won an arbitral award of $1.17 billion against the Tata Group from London's commercial court on July 25.

The Tatas have already filed a suit in Delhi High Court to pre-empt the enforcement of the London court's award. Docomo, in turn, has filed suits in London and New York staking claim to the Tata Group's overseas assets to realise the money.

The Tatas had refused to pay Rs 7,250 crore to the Japanese company - half the value of Docomo's original investment of $2.5 billion in March 2009 - by exercising a put option at the end of five years. The Tatas had claimed that the RBI had refused to grant permission to make the payment under new rules put in place in January 2014 on the pricing of options linked to equity instruments.

Docomo had insisted on being paid Rs 58 per share for its holding in Tata Teleservices under the terms of the agreement. However, the Tata group offered Rs 23.34 a share in line with RBI guidelines that said an international firm could only exit its investment at a valuation "not exceeding that arrived at on the basis of return on equity".

Mistry said he had "always mentioned that the Tatas should honour all commitments within the law. This stance is based on Tata Sons' board view and was always consistent with the series of board meetings in which the Docomo issue was discussed."

The handling of the $1.17-billion compensation slapped by an arbitration panel over breach of agreement with Docomo is said to be one of the triggers for Tata Sons sacking Mistry last month.

Last week, the Financial Times reported that in July, Tata had written a letter to Ryuji Yamada, NTT Docomo's former chief executive, in which he expressed regret that that their joint investment had "degenerated" into conflict. He apparently added that such a situation would never have happened if they had remained in charge of their groups.

In 2014, NTT Docomo had written down the value of its investment by 51 billion yen (about Rs 3,250 crore).

Mistry's latest letter clearly seems to be in response to Tata's efforts to distance himself from the decision-making in the Docomo case.

"Ratan Tata and N.A. Soonawala participated in separate meetings with Mr Mistry," the letter said.

"They also participated in the meeting with the legal counsel (who also happened to be a trustee of the Dorabji Tata trust) and who represented Tatas in the litigation." The trustee in question was Darius Khambata.

"At all times, Ratan Tata and Soonawala concurred and approved the course of action adopted by the Tatas and as advised by the legal counsel," the Mistry letter said.

In his letter to employees, interim chairman Ratan Tata said: "The decision to change the leadership of Tata Sons was a well-considered and serious one for its board members. This difficult decision, made after careful and thoughtful deliberation, is one the board believes was absolutely necessary for the future success of the Tata Group."

Ratan Tata, 78, who retired as Tata Group chairman nearly four years ago, justified his return to maintain "stability and continuity of leadership" and promised to give the group "a world-class leader" when a full-time boss is appointed. Responding to Mistry's latest statement, a Tata group spokesman said: "The insinuations are being imagined and this (Docomo) matter is sub-judice."

Ratan Tata, in his second letter to employees after the October 24 sacking of Mistry, said the group companies should focus on their profit margins and their market position and not compare themselves to their past.

"The focus has to be on 'leading' rather than 'following'," he wrote.

N.S. Rajan and Nirmalya Kumar resigned as non-executive directors on boards of Indian Hotels Company and Tata Chemicals respectively, days after the group executive council formed by Mistry was disbanded.

Rajan, Kumar and Madhu Kannan, another member of the erstwhile GEC, had quit the Tata Group last week.