The Taoiseach has said any damage done to Ireland's reputation over the horse meat controversy will be quickly reversed as a result of swift action taken to determine the source of the problem.

Enda Kenny said Ireland has acquired a reputation internationally for the very highest standards and it is always a source of concern when an issue like this arises.

He said an investigation is ongoing to determine the source of the common additive to the products produced by the three plants in question.

The Taoiseach said it is vital that in a country that exports €9bn worth of food products that the produce is of the highest standard.

His comments come after tests revealed the presence of horse DNA in nine out of 13 samples of finished burgers at the Silvercrest Foods plant in Ballybay, Co Monaghan.

Earlier, Minister for Agriculture Simon Coveney said he did not know how long horse meat DNA has been present in some Irish beef burgers.

Speaking on RTÉ's Morning Ireland, Mr Coveney said good progress is being made in identifying the source of the problem.

Mr Coveney said the tests are helping his department to establish where the problem originated.

He said the department has its "suspicions" about where the horse DNA came from and he said it was acting on those suspicions.

This afternoon, the EU Commission said Irish authorities have informed it about the problem, but it is not an issue that the commission will get involved in.

A spokesperson for the EU Commissioner for Health and Consumer Policy said it had come to the decision as no food safety issue had arisen and no regulations had been breached.

The commission spokesperson said that the controversy was a business-to-business issue that appeared to have involved mis-labelling.

Production suspended

ABP Food Group, which owns the Silvercrest plant in Ballybay, said it has temporarily suspended production with immediate effect.

The department said test results from Liffey Meats in Ballyjamesduff in Co Cavan have not yet been completed.

Tests were also carried out on raw ingredients from the Silvercrest Foods plant.

Of the seven samples of raw ingredients tested, one was positive and came from another EU member state, though the Department of Agriculture would not say exactly where.

The tests on all of the ingredients in the burgers that were sourced from Irish suppliers were negative.

Further tests will be carried out in Germany on the positive samples from the plant to establish the percentage of horse DNA present.

In a statement last night, the ABP Food Group said its investigations have centred on two third party EU suppliers.

It said it has established that one of these suppliers was the source of the contaminated material.