"Private companies buying Vietnamese rice may have run into trouble as rice prices have risen in the past month," a Vietnamese trader at a foreign company in Ho Chi Minh City said.

He said the affected volume may total 150,000 tonnes. Other traders could not confirm the figure but said the risk of delays or defaults was real.

Vietnam's 25 percent broken rice, often bought by the Philippines, has risen 2.3 percent to $450 a tonne, free-on-board basis, this week from $440 in early March when private firms in the Philippines arrived to seek Vietnamese grain