Glencore and Xstrata have announced the third extension of the completion date for their $33bn [£22bn; €25bn] merger as they await the results of a competition probe in China.

The world's biggest publicly traded commodities firm said Tuesday on its website that it has set a 16 April "long stop" date for its merger with Xstrata. The group also said full-year earnings fell 17 percent to $4.5bn, whille net income fell 25 percent to $3.06bn, largely in line with analysts' expectations.

Xstrata, the world's fourth largest mining group, saw earnings tumble 79 percent to $3.65bn thanks to $2.6bn in impairment charges linked to its mining operations in Canada and Australia.

"Outside of our robust financial performance, 2012 also saw some major strategic landmarks for Glencore," said CEO Ivan Glasenberg, who will also lead the combined group when the merger is completed.

"Most importantly, we commenced the process to reunite Xstrata with Glencore following a decade in the public markets. We continue to work on closing the merger with Xstrata. Completion of the merger remains conditional upon the receipt of the outstanding regulatory approval in China."

China's Ministry of Commerce, known as Mofcom, is the final national regulator yet to approve the merger, after earlier sign-offs from authorities in Europe and South Africa. Glassenberg told investors on a conference call immediately after the results that he does not have any major concerns over the Mofcom approval process.

Glencore shares closed at 369.95 pence each in London Monday after a 1.86 percent fall on the session. Xstrata shares fell 2.44 percent Monday to close at 1,099.5 pence each.