Tesco, Britain's biggest retailer, said on Monday it had found horse DNA exceeding 60 percent in some of its own-brand frozen spaghetti bolognese meals withdrawn from stores last week.

Tesco said tests carried out since pulling the product last Wednesday had identified the presence of horse DNA, with most positive results at a trace level of less than one percent. However, three tests showed horse DNA levels of over 60 percent.

None of its tests were positive for the potentially harmful drug known as bute - a common, anti-inflammatory painkiller for sporting horses but banned for animals intended for eventual human consumption, it said.

The news is the latest installment in a scandal that has rocked the food industry in Britain and across Europe. Investigations into suppliers have been launched in recent weeks after the discovery that beef products sold to some of Britain's major supermarkets and fast-food chain Burger King contained horsemeat.

Tesco had already dropped an Irish supplier of frozen beef burgers that had also tested positive for horse DNA.

The firm had pulled its frozen Everyday Value Spaghetti Bolognese product last week as a precaution after the manufacturer Findus withdrew its beef products on the advice of its French supplier Comigel, which also supplies Tesco.

Findus said last week that some of its beef lasagne meals had contained horse meat.

On Monday, Tesco said the source of the horse meat was still under investigation by the relevant authorities, but added that it would not take food from Comigel's facility again.

"The level of contamination suggests that Comigel was not following the appropriate production process for our Tesco product and we will not take food from their facility again," Tesco said, adding that it h