Chinese firm Hanlong Mining on Tuesday announced it had reached an agreement to buy Australia's Sundance Resources, after sweetening its offer to Aus$1.65 billion (US$1.57 billion).

Hanlong made a 50 cents per share bid in July to take over Perth-based Sundance, an iron ore, copper and gold miner with projects in central Africa.

It revealed Tuesday it will acquire 100 percent of Sundance shares through a scheme of arrangement, after lifting its offer to 57 cents cash per share. Sundance shares last traded at 43 cents.

"The board of Sundance has unanimously recommended the offer in the absence of a superior proposal and subject to an independent experts report," Hanlong said in a statement.

The offer remains subject to a number of conditions, including approval from Australia's Foreign Investment Review Board and China's National Development and Reform Commission and Hanlong securing approved financing.

News of the agreement comes as three former Hanlong executives are being investigated by Australia's corporate watchdog on claims of insider dealing related to the proposed investment in Sundance and uranium explorer Bannerman.

Hanlong Mining itself is not under investigation and has said it is cooperating fully with the Australian Securities and Investments Commission (ASIC) investigation.

Liu Han, chairman of Hanlong parent company Sichuan Hanlong Group, welcomed the new agreement which he said allowed Sundance shareholders to realise a "substantial premium for their investment".

"Today's agreement will also bring great benefits to the people of the Republic of Cameroon and the Republic of Congo through the additional certainty it brings to the development of the Mbalam and Nabeba projects," he said.

Liu said Hanlong, which already holds about 18 percent of Sundance shares, was committed to investing in Australia and Australian resources companies as it seeks to build a global, diversified mining company.

Beijing's interest in Australia's mining firms has sparked intense debate in the country over whether to allow Chinese state-owned entities to increase their control over its resources.