HANOI (Dow Jones)--Vietnam will export 4 million metric tons of rice this year, down from a target of 4.5 million tons set by the government earlier this year, said Prime Minister Nguyen Tan Dung .

  The country will only export 3.2 million tons of rice by the end of September, Dung said in the statement published Sunday on the government's Web site.

  Vietnam has to limit the export volume of rice "to maintain food security and prevent excessive price rises," Dung noted. 

"The government is asking the Ministry of Finance to consider applying a tax on rice exports," he said.

  Currently Vietnam exempts rice exports from taxes.

  This is the first time the prime minister has adjusted the export quota for rice this year.

  Vietnam is estimated to have exported 859,000 tons of rice valued at $366 million in the first quarter this year, with volume up 5.3% on year and value 43% higher, according to government data.

  In 2007 the country exported 4.5 million tons valued at $1.454 billion, down 3.1% on year in volume, but up 13.9% in value.