DHAKA (REUTERS) - Customs authorities in Bangladesh have restricted the import of more than 600 tonnes of powdered milk mainly from New Zealand-based Fonterra, pending mandatory chemical tests, a senior official said on Tuesday.

Fonterra, the world's biggest dairy exporter, was caught up in a contamination scare this month after it found bacteria in some of its products that could cause botulism. It also disclosed it had to withdraw 42 tonnes of milk powder bound for China because of high nitrite levels.

The move by Bangladesh comes after the commerce ministry asked customs officials in the port city of Chittagong to exercise caution in releasing any Fonterra-branded dairy products. In the year to June, Bangladesh imported 20,741 tonnes of milk powder, mainly from Fonterra.

"We decided not to deliver any milk powder from Fonterra without a chemical test as there might be nitrate in the milk powder," said Mr Mahabub Ahamed, secretary of the Ministry of Commerce. "If poisonous nitrate is found, we will ban the milk powder," he told Reuters.

Mr Karmrujjaman Kamal, marketing director of Pran Dairy Ltd, an importer, said Fonterra officials had agreed to take back any contaminated milk powder.

Fonterra officials in New Zealand were not immediately available to comment.

Sri Lanka last week ended a ban on the sale of Fonterra milk products that had been ordered after food safety authorities said they found the toxic farm chemical dicyandiamide (DCD) in two batches of milk powder.

The term nitrates is often used interchangeably with nitrites, which occur naturally in water, soil and food and can be used as fertilisers and preservatives. Excessively high levels can be toxic.