HANOI -- Vietnam's trade minister on Friday called on the country's rice exporters to honour their export contracts to maintain demand despite a recent surge in prices for the staple grain, state media reported.

Prices of Vietnam's 5% broken rice RI-VNBKN5-P1 rose to a 15-year high of $590-$600 per ton on Friday, up from $550-$575 a week ago, traders said, after India on July 20 ordered a halt to its largest export category to calm domestic prices.

Two trade sources said earlier this week that some rice exporters in Thailand and Vietnam were re-negotiating prices on sales contracts for around half a million metric tons for August shipments as India's ban tightens global supplies.

"We need to stick to the signed contracts to protect our reputation," trade minister Nguyen Hong Dien said at a conference, according to Tien Phong newspaper.

Dien called on exporters to focus on ensuring rice quality and avoiding an excess of exports to maintain sufficient domestic supplies and fully meet reserve requirements.

"It's unacceptable for a rice exporting country to face tight supplies and high domestic prices," Dien told the conference.

Vietnam's rice paddy output is expected to rise to 43 million tons this year from 42.7 million tons last year, the head of the country's Department of Crop Production said on Tuesday.

Rice shipments from Vietnam, the world's third-largest exporter after India and Thailand, are expected to reach 7.8 million metric tons this year, up from 7.1 million tons recorded last year.

Exports in the first seven months of this year were estimated to have risen about 18.7% from a year earlier to 4.84 million metric tons, according to preliminary government data.