BHP Billiton chief Marius Kloppers launched a contemptuous attack on its takeover target Rio Tinto on Wednesday, after reporting figures that showed BHP's iron ore production was at a record high and criticized Rio's growth projections.

BHP ,the world's largest resources company who is trying to buy rival Rio Tinto for about $150 billion, has consistently outperformed its rival, Kloppers said in an interview with Financial Times.

Kloppers said Rio had missed the boat in previous years when it came to capturing the full potential of the resources boom, and questioned growth projections released by Tom Albanese, Rio's CEO.

After unveiling BHP's March quarter results which showed the company was on track for yet another record result, Kloppers said BHP had consistently outperformed Rio in the past.

It must be terrible (for Rio) that every quarter, BHP outperforms, and that has been the case for seven years, Klopper said.

BHP's iron ore division outpaced Rio, with a 22 percent gain in output to a record 28 million tones in the first-quarter, compared to the same period a year earlier. Meanwhile, Rio's first-quarter production figure grew by only 16 percent, after its operations were affected by tropical cyclones and power cuts.

However, BHP reported mixed production results elsewhere, with quarterly losses in aluminum, copper, nickel and diamonds.

Klopper also criticized projections Rio released in February predicting its annual compound growth in production volume would more than double BHP's between this year and 2015 to 8.6 percent, against a 3.9 percent rate for BHP.

That is not a scorecard, it is a wish list, Kloppers said, What Tom is putting out there has no basis to be verified with acceptable norms in our industry.

Meanwhile, Rio Tinto's chairman Paul Skinner told shareholders that the board had rejected the BHP Billiton bid as it significantly undervalued the company's assets and potential, according to the Sydney Morning Herald.

The board will not engage in discussion with any party whose proposals do not fully value Rio Tinto, Skinner said.

We have an outstanding portfolio of assets; our business is performing very strongly and is very well managed by a talented team.