Serbia has declared water from the river Danube safe following a spill which contaminated it with cyanide and killed thousands of fish.

It lifted its ban on the use of water from the river on Friday, saying levels of the poisonous chemical were now below allowable amounts.

The cyanide was blamed on a spill from a Romanian gold smelter, half owned by Australia's Esmeralda Exploration Ltd.

The pollution was carried by the river Tisza, the Danube's largest tributary which flows through Hungary and into Serbia.

"In water samples taken on February 17 in the Tisza and the Danube cyanide was found only in traces," said a statement from the ministry in charge of water resources.

The World Wide Fund for Nature said on Friday that the ecological impact of the spill would not be known until the end of the year.

It said otters and white-tailed eagles in Hungary, both protected species, had been badly affected by the spill.

Overseas aid

Otters died after eating the contaminated fish and the WWF says the whole food chain could suffer.

On Friday, the US and Australia both offered to help Hungary clean up the pollution of the Tisza river.

The Hungarian ambassador to Canberra, Istvan Gyuerk, said: "Australia is ready to offer to Hungary, scientific and technological help in averting the consequences of the catastrophe."

Thomas Robertson, charge d'affaires at the US embassy in Budapest, said they contacted the Hungarian Government to offer assistance as soon as they heard of the disaster.

"The US Government has expressed deep concern over the environmental disaster," he said.

The European Union is to send international experts to the area to find out what happened and how such a catastrophe can be prevented in future.