The carmaker said its inquiry had concluded that some of Raj Nair's conduct had been "inconsistent with the company's code of conduct".

Ford did not specify why the investigation was started nor what it uncovered.

Mr Nair said in a statement that "I sincerely regret" certain behaviour.

Ford President and Chief Executive Jim Hackett said in a statement: "We made this decision after a thorough review and careful consideration. Ford is deeply committed to providing and nurturing a safe and respectful culture and we expect our leaders to fully uphold these values."

Mr Nair had been President of Ford North America since 1 July. He was previously head of global product development and chief technical officer.

He apologised, without elaborating on the reasons for his going.

"I sincerely regret that there have been instances where I have not exhibited leadership behaviours consistent with the principles that the company and I have always espoused," Mr Nair said.

He added: "I continue to have the utmost faith in the people of Ford Motor Company and wish them continued success in the future."

A spokesman for the US's second biggest carmaker said the company would not be commenting on the nature of Mr Nair's departure.

'Rising star'
In August, Ford agreed a multi-million-dollar settlement after an investigation into sex and race harassment at two factories in Chicago.

The inquiry was conducted by the US Equal Employment Opportunity Commission, which said female and African-American employees had been subjected to sexual and racial harassment and found the carmaker retaliated against employees who complained about the harassment or discrimination.

In an open letter about the matter, Mr Hackett wrote "there is absolutely no room for harassment at Ford Motor Company.... We don't want you here, and we will move you out for engaging in any behaviour like this."

Michelle Krebs, an analyst at Autotrader, said the departure of Mr Nair, a "rising star" who had been with the carmaker for 30 years, comes at a "particularly bad time" for Ford.

She told the Reuters news agency: "Investors and analysts have been unhappy with the seeming lack of a clear direction for Ford, especially in terms of future mobility services.

"The stock price has fallen. The pressure is on Jim Hackett, anointed CEO last spring, to lay out a clear road ahead for Ford."