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The chief executive of Infosys, Vishal Sikka, has resigned from his post with an unconventional and lengthy letter blaming "personal attacks".

In the letter Mr Sikka said the "continuous drumbeat of distractions" contributed to his decision to resign.

It follows public criticism of the company and its board by its founders.

Infosys is one of India's largest IT services firms. Shares in the firm plunged 9% following news of Mr Sikka's departure.

Mr Sikka was appointed in June 2014 and tasked with turning around the struggling business.

The company announced he was resigning as chief executive and managing director with immediate effect, but would stay on as executive vice chairman.

Infosys chief operating officer U. B. Pravin Rao will take over as interim chief executive, the firm said.

'False' allegations

The move follows disagreements between the company and its founders, who were unhappy with various decisions taken by the board.

The firm's founders, who still own 12.75% of Infosys, had questioned a pay rise granted to Mr Sikka and the size of severance payouts given to other employees.

In his resignation letter, Mr Sikka covers a wide range of topics - from artificial intelligence, to the Charlottesville tragedy, Brexit and US President Donald Trump - as he explains his decision to step down.

He notes constant "distractions" frustrated his efforts to grow the company.

"Over the last many months and quarters, we have all been besieged by false, baseless, malicious and increasingly personal attacks," he said.

"This continuous drumbeat of distractions and negativity over the last several months/quarters, inhibits our ability to make positive change and stay focused on value creation.

"Allegations that have been repeatedly proven false and baseless by multiple, independent investigations," he wrote.

Under Mr Sikka's leadership the firm, which exports IT services, has shifted away from traditional IT services to focus on new products.

Some parties, including the company's founders, have been critical of the approach.

Analysis: Sameer Hashmi, India business reporter

The bitter acrimony between the board and Infosys founders had been brewing for some time. But Mr Sikka's decision to quit the company under these circumstances has left investors and shareholders worried.

In his first comments to analysts following his resignation, Mr Sikka described the continuous allegations against him by the founders headed by Mr Narayana Murthy as 'sickening'. The Infosys board has backed Mr Sikka and squarely blamed Mr Murthy - the main founder of the company - for Mr Sikka's resignation.

Infosys has been grappling with challenges the IT industry has faced in recent years. With the Trump administration cracking down on H1-B visas, which were primarily issued to Indian IT employees, profits of Indian IT firms have been under pressure.

The US is a significant market for the Indian IT industry, contributing more than 60% to overall revenues. There's also the rise of artificial intelligence, which has led to massive job cuts at Indian IT firms.

Allegations 'harmed morale'

In a statement, Infosys said it was "profoundly distressed" by the personal attacks on its management team in recent months.

The company denounced its critics and said the allegations had "harmed employee morale and contributed to the loss of the company's valued CEO".

It praised Mr Sikka's efforts in providing a new direction for the company, increasing revenues and reducing employee attrition.

Mr Sikka will receive an annual salary of $1 in his new role as executive vice chairman.