LONDON (Reuters) - The new chairman of BHP (>> BHP Billiton Plc) (>> BHP Billiton Limited), the world's biggest miner, threw his weight behind his CEO on Thursday after attacks from activist investor Elliott Advisors prompted speculation that the end of Andrew Mackenzie's tenure was imminent.

Pressure has mounted on BHP and its chief executive since Elliott went public in April with its criticisms of the miner's strategy.

"Any suggestion there is a set timeline around Andrew's tenure is simply false and without merit," Chairman Ken MacKenzie told reporters after his first AGM since taking office at the start of September.

Asked by a shareholder whether it was Elliott or the BHP board that was running the company, the chairman replied that "MacKenzie and Mackenzie" were running BHP, although he did not specify the order of the pair who share the same names, but with slightly different spelling.

At least five representatives from Elliott Advisors, which holds 5 percent of BHP, attended the London meeting but did not ask questions from the floor.

Elliott declined to comment on Thursday, but it has welcomed the new chairman's appointment.

Chairman MacKenzie said he had met more than 100 shareholders across eight countries, which he said gave him confidence, though he added that there are areas where the company needs to sharpen its focus.

He reiterated work is in progress to sell shale assets, which is one of Elliott's main demands, and that further action would take place to refresh the board of directors.

SKILLS REVIEW

"We recognise that the board needs to continue to evolve to take into account the rapidly changing environment in which we operate. So we will undertake a review of the board's skills and experience requirements during this financial year," he said.

BHP's London share price has risen nearly 7 percent since the start of the year, about half as much as that of its main rival Rio Tinto. (>> Rio Tinto) (>> Rio Tinto Limited)

Both the chairman and the CEO said they were striving to maximise shareholder value and that meant shale assets would be sold only at the right price.

"We will be both urgent and patient as we examine all the options," CEO Mackenzie said. "We have to get the timing right to maximise shareholder value."

BHP's big rival Rio Tinto suffered a setback this week when the U.S. Securities and Exchange Commission (SEC) charged the company and two of its former executives with inflating the value of coal assets in Mozambique and concealing critical information. The company said it would defend itself vigorously against the allegations.

One shareholder asked BHP to exit its partnership with Rio to develop the Resolution copper mining project in Arizona. Rio is the majority shareholder.

"We're talking about a potential project," CEO Mackenzie said. "It has not been decided to go ahead."

Rio Tinto in an emailed comment said it was "fully committed to advancing the Resolution project".

Chris LaFemina, a mining specialist at Jefferies bank, said he had preferred Rio over BHP for the past two years.

"While our preference has not changed, BHP's competitive position has modestly improved," he said in a note.

"New chairman Ken MacKenzie seems willing to push for significant strategic changes at BHP ... after years of unacceptable underperformance of its share price versus Rio's."

(Editing by David Goodman and Elaine Hardcastle)

By Barbara Lewis and Zandi Shabalala