US and Vietnamese talks on trade have become bogged down by a dispute over catfish.

The deputy prime minister of Vietnam, Nguyen Tan Dung, has criticised the United States for a new law restricting the imports of Vietnamese catfish, after returning from a visit there.

The dispute is the first bilateral trade row since relationships between the two countries became normalised.

The deputy prime minister's visit was the first by a high-ranking Vietnamese delegation since the Bilateral Trade Agreement was approved earlier this year.

Delta fresh

Tthe US Senate moved to block catfish imports earlier this week by specifying that only a limited number of species can be labelled catfish.

US catfish production is one of the world's largest aquaculture industries.

Vietnamese farmers - keen to reduce their reliance on rice production - have taken an increasingly large stake of that market.

The introduction of the law follows concerns about hygiene - since dismissed by visiting US officials - and concerns about trademarks.

Part of the problem is that Vietnamese catfish is often referred to as Delta Fresh, confusing buyers who think they are buying US produce.

In fact it is from the Mekong Delta in southern Vietnam.

Protectionist behaviour?

"I think it has made a lot of Vietnamese angry.

"They look at the situation and think this is protectionist behaviour on the American side, yet we just agreed to ratify a trade agreement which pushed for open trade... there is a bit of hypocrisy," Mekong Research's Sam Korsmoe told the BBC's World Business Report.

The trade embargo against Vietnam was only lifted by President Clinton in 1994.

With a population of 80 million, Vietnam is the world's 14th most populous nation, but trade with the US amounted to only $1.2bn last year.

Analysts expect that this could more than double with normal trade relations.