HANOI, Vietnam/MANILA, Philippines -- Vietnamese exporters halted trade in a popular grade of rice on Wednesday after traders said the Philippines had agreed to buy one million tons of the grain from Vietnam, although Manila remained tight-lipped about the deal.The Philippines is the biggest rice buyer on international markets and imports about 10 percent of its annual needs. Its purchases of 2.3 million tons last year propelled rice prices to historic highs and set off a global food crisis.

Traders in Vietnam and in the Philippines said on Tuesday the agreement was for the sale of 1 million to 1.5 million tons of rice starting February, and that the price was set at $380 per ton, including cost and freight.

"Let's just wait for any government supplier to make their own official statements," Philippine Agriculture Secretary Arthur Yap said in a mobile phone text message when asked about the deal to secure supplies of the national food staple.

But he added: "Our food security stock commitments are well in place for 2009."

Manila has been careful to avoid a repeat of last year's scenario and the government-to-government deal with Hanoi, the world's second-biggest exporter, will secure the bulk of its 1.5 million ton import needs for 2009.

The Vietnam Food Association's general secretary, Huynh Minh Hue, also offered no comments on the deal.

But Vietnamese exporters stopped quoting prices for the popular 25-percent broken grade of rice following the reports.

"The 25-percent broken grade is now the ban zone," said one trader, adding that a floor price set for the grade at $370 per ton, free on board, about 7.0 percent above current market levels of $345 per ton, was also a factor.

The food association also set floor prices of $400 per ton for 5.0-percent brokens, $390 per ton for the 10-percent brokens and $380 for the 15-percent brokens, free on board.

Vietnamese farmers will start harvesting the largest crop of the year in March, mostly higher-quality 5.0-percent brokens and 10-percent brokens.

A Philippine-based trader had said the Vietnam deal included both the 25-percent broken and 5.0-percent broken grades but could not give specific details.

In Bangkok, benchmark rice prices rose for the second consecutive week, reaching $580 per ton, but traders said the reported Vietnam-Philippines deal was not a factor.

Exporters said prices were supported by demand for loading to several countries in Africa and Asia.

"Several ships are waiting to load fragrant rice to China and parboiled rice to Africa," one trader said. Another said prices were supported by a government buying scheme.

The prices of the benchmark Thai 100 percent B grade rice soared to $1,080 per ton in April last year at the height of the food crisis, sparked by the Philippine purchases and export curbs by major producers.

Rice is a staple for half the world's population and the surge triggered global protests and threatened hunger for nearly one billion people.

Prices have been declining steadily since then, but still remain substantially above the $400 per ton or lower typical since the start of the decade.