Vietnam's trade minister on Friday said a surge in global rice prices offered an opportunity to increase exports, but stressed the need to ensure domestic food security.

Prices of Vietnam's 5% broken rice hit a 15-year high of $590-$600 per metric 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.

"This is an opportunity for us to boost rice production and exports," Minister of Industry and Trade Nguyen Hong Dien said at a conference, according to a statement on the ministry's website.

Vietnam, the world's third largest rice exporter after India and Thailand, is expected to export 7.8 million metric tons of rice this year, up from 7.1 million tons last year, an agriculture minister official said on Tuesday.

Its rice paddy output is expected to rise to 43 million tons from 42.7 million tons, the official added.

Dien on Friday also called on the country's rice exporters to honour export contracts signed before the recent price surge to maintain demand, and seek to sign new contracts based on the "current market conditions".

"We need to stick to the signed contracts to protect our reputation," Dien said.

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 shipment as India's ban tightens global supplies.

He 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 was quoted by state media as saying at the conference.

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. (Reporting by Khanh Vu; Editing by Kanupriya Kapoor and Jan Harvey)