NEW YORK - Moody's Investors Service on Monday lowered its credit outlook for Germany, the Netherlands and Luxembourg from stable to negative, warning that the three European countries could lose their top AAA ratings.

However, the rating agency affirmed Finland's AAA rating and stable outlook.

It said in a statement that all the four countries are adversely affected by the ongoing European debt crisis, but Finland maintained its top rating and stable outlook partly because of its small and domestically oriented banking system.

Moody's explained that the downgrading was based on the risk of Greece's exit from the eurozone, which would pose a "material threat" to the single currency.

Even if the Greeks decide to stay in the zone, the contingent liabilities taken on by the strongest eurozone countries are rising, said the statement.