TOKYO: Japan's farm ministry said Saturday that it had found a cow backbone in a shipment from the United States that violates a ban imposed due to concerns over mad cow disease.

A Japanese importer on Friday informed the ministry that it had received a box containing 16 kilogrammes (35 pounds) of US beef without sanitary certification, a requirement under a trade accord between the two countries.

The ministry later confirmed that it was Japan's third discovery of US cow backbone designated as specified-risk material since Tokyo conditionally lifted a ban on US beef shipments in 2006.

The ministry has suspended imports from the shipping agent and immediately called on the US Department of Agriculture to investigate the case, officials said.

Japan banned US beef in December 2003 after the brain-wasting cattle disease bovine spongiform encephalopathy (BSE) was found in a US herd. Japan had until then been the US cattle industry's biggest export market.

The ban nearly grew into a full-blown trade war, with US farm-state senators pressing for sanctions unlessTokyo opened up its markets by the end of 2005.

Japan agreed in 2006 to resume US imports on condition age and portion limits be imposed on cattle at the time of slaughter.