Standard and Poor's will decide whether or not to downgrade euro zone countries in the coming days following an EU agreement to forge tougher fiscal rules, the rating's agency's head in France said Friday.

S&P said earlier this week that it would decide whether to downgrade 15 euro zone countries, including Germany and France, depending on whether an EU summit in Brussels Thursday and Friday produced a convincing response to the debt crisis.

With the excerption of Britain, EU countries agreed at the summit to draft a new treaty creating a tougher fiscal regime and closer economic integration.

S&P's Carol Sirou told French radio BFM Business that the ratings agency would analyse the impact of the agreement on confidence in the economy and financial markets.

S&P would also consider whether the agreement might prompt the European Central Bank to play a more aggressive role in tackling the crisis before taking a downgrade decision, she said.

It (the decision) will be in the coming days once we have all the necessary elements and reflection, she said.

(Reporting by Leigh Thomas; editing by Ron Askew)