Australian coal miner Macarthur Coal on Monday refused to back a US$5.3 billion takeover offer from steel giant ArcelorMittal and US company Peabody Energy, calling it opportunistic. Peabody and ArcelorMittal had initially offered A$15.50 per share but during due diligence agreed to boost this to A$16, subject to Macarthur agreeing not to talk with other potential suitors. Macarthur, the world's largest miner of pulverised coking coal, said in a statement to the Australian stock exchange that it rejected the bid because it wanted to keep talks with others open. "The offer appears to be an opportunistic attempt to acquire Macarthur at a time of global economic volatility and regulatory uncertainty in Australia, and fails to reflect Macarthur's industry-leading position," chairman Keith DeLacy said. The company added: "While there can be no assurance that a superior proposal will emerge, Macarthur's directors consider it is clearly in shareholders' interests to do all that they can to facilitate this." Macarthur shares rose 1.61 percent to Aus$15.80 in early trade.