De Beers, supplier of about a third of the world’s rough diamonds, said prices of the gems may “stick” at current levels after demand from India and China spurred a more than 35 percent rally this year.

Increasing wealth in the two countries’ expanding economies is enabling consumers to buy more diamond jewelry, compensating for slower growth in the U.S., the biggest retail-gem market. Demand from East Asia caused a supply shortage, Chief Executive Officer Philippe Mellier said.

“We’re now reaching a new plateau from which prices are going to oscillate,” Mellier, 56, said in an interview by phone from London yesterday. “I am expecting this new level of pricing to stick.”

Mellier, a former Alstom SA executive, was appointed as the leader of De Beers in May, marking a break with the tradition of promoting from within as the Johannesburg-based company sought to recover from the global economic crisis that had forced it to slash prices and idle mines. The company is 45 percent held by Anglo American Plc, 40 percent owned by South Africa’s Oppenheimer family and 15 percent controlled by the government of Botswana.

While retail sales in India and China are “very, very strong” sales in the U.S. are growing, defying expectations of a decline, Mellier said.

“All the numbers we are receiving from the U.S. from our partners, from our own stores are telling us that the sales are up, not hugely up, but up,” he said.

De Beers estimated in February that the U.S. bought about 38 percent of diamond jewelry in 2010, with India making up about 10 percent and China and Hong Kong a combined 11 percent.

‘Strong’ 2012 Start

“We don’t see any softening of the demand,” Mellier said.

De Beers should produce record or near-record sales in 2011, RBC Capital Markets London-based analyst, Des Kilalea, said in a note to clients earlier this month. RBC forecasts sales by De Beers’ trading arm at about $6.4 billion this year, the second highest on record. De Beers holds sales known as ‘sights’ for exclusive customers.

“Our feeling, without sounding too optimistic, is that retail is generally strong,” Mellier said, in reference to global sales. “Therefore, we will see some appetite for our sights at the end of the year and certainly a pretty good start next year because there is strong demand from Asian customers.”

Russia’s OAO Alrosa, De Beers’ biggest rival, said yesterday that average sales prices rose 30 percent to $109 a carat in the first half of this year, compared with $84 over the whole of 2010.

De Beers had record earnings before interest, tax, depreciation and amortization of $1.4 billion in 2010 following a 57 percent surge in its trading arm’s sales to $5.08 billion.

The company will probably produce 33 million carats to 35 million carats this year compared with 33 million carats last year, Mellier said. A carat is equivalent to a fifth of a gram.

De Beers mines diamonds by itself or in joint ventures in South Africa, Canada, Botswana and Namibia.