LONDON (Reuters) - Anglo American Plc (>> Anglo American plc) has warned it will likely take a charge on last year's results, becoming the first major mining group to explicitly acknowledge the impact of recent falls in prices of iron ore, coal and other commodities.

The company, which also posted annual production slightly ahead of guidance for key commodities, said it expected to take certain one-off non-cash impairments but gave no figures for the likely hit.

Its shares, up 1.2 percent at 1,103.5 pence by 10:09 a.m., remained not far from a near six-year low of 1,029p set earlier this month.

Anglo, whose shares have lagged rivals for much of the past decade, is undergoing a restructuring focused on improving mining operations and selling less profitable assets. But its turnaround efforts are clashing with a rout in prices of copper, coal and iron ore, which make up much of its earnings.

A flood of new iron ore supply from major miners BHP Billiton (>> BHP Billiton plc) and Rio Tinto (>> Rio Tinto plc) has smothered demand growth and hammered prices in the last year, hitting their smaller and higher-cost rivals.

Analysts expect Anglo to take charges of between $1 billion (658 million pounds) and $5 billion relating specifically to its costly Brazilian iron ore project Minas Rio and its Australian coal operations.

Other large miners such as Glencore (>> Glencore PLC) and BHP Billiton are also expected to announce impairments on the back of the oil and metals price rout, but to a smaller degree.

Rio, which derives most of its earnings from iron ore, is likely to prove the most shielded from impairments for now, due to the higher quality of its iron ore assets, analysts said.

"I think Anglo is the one likely to have the biggest headline number," said analyst Jeff Largey at investment bank Macquarie. "On coal it has some assets that are positioned poorly on the cost curve. And Minas Rio is a very high quality asset, but it's more to do with what you spent to develop it against what you expect to earn."

Minas Rio, the biggest-ever foreign investment in Brazil, had been plagued by delays and cost overruns since Anglo bought it in 2007-2008 for about $5.5 billion.

The project will end up costing about $8.4 billion. Iron ore prices in the meantime have plunged from a peak of almost $200 a tonne in 2011 to just above $60 this week.

Anglo beat its output targets, with production of iron ore for instance, its biggest earner, up 14 percent to more than 48 million tonnes at its Kumba subsidiary, slightly ahead of its 47 million tonne target. Minas Rio added a further 688,000 tonnes.

In December it warned of a delay in reaching a return on capital target and on Friday, its platinum and iron ore units flagged sharp falls in full-year earnings.

(Editing by Jason Neely and David Holmes)

By Silvia Antonioli