Singapore state investor Temasek Holdings has taken a 5.5 per cent stake in Canada's Ivanhoe Mines valued at US$426 million (S$544), increasing its bet on resources firms.

Temasek owned 40.855 million shares of the Vancouver-based firm, the Singapore investor said in a filing to the US Securities and Exchange Commission on June 8.

A source familiar with the deal said Temasek had a small stake in Ivanhoe, which is controlled by mining giant Rio Tinto , but has increased its holding through market purchases.

A Temasek spokesman confirmed the filing but did not provide details.

Ivanhoe last month launched a rights offering to raise US$1.8 billion as part of a comprehensive financing plan to continue development of its Oyu Tolgoi copper-gold project in Mongolia.

Temasek, which has about 36 per cent of its assets in financials, has been slowly increasing its investments in resources firms. In April it bought shares of PetroChina Co's unit Kunlun Energy Co Ltd.

Sovereign investors, hurt by investments in Western banks during the 2008 financial crisis, have moved away from financial services into sectors such as commodities and infrastructure.

Earlier this year, the Government of Singapore Investment Corporation, one of the world's biggest sovereign wealth funds, bought a 5 per cent stake in commodities trader Bunge Ltd worth around US$500 million.

At Temasek, energy and resources accounted for only 3 per cent of its US$150 billion in assets as of March 2011.

Temasek also owns a small stake in Chesapeake Energy Corp. The US gas firm is under fire from investors after Reuters reported its chief executive Aubrey McClendon arranged for more than US$1 billion in personal financing - from a lender who is also a big source of funding for the company - in a situation that may put his interests at odds with those of shareholders.