The euro reversed earlier losses to trade strongly in overnight trading, reaching a 2-week high against the US dollar Wednesday morning. Investors lifted the single currency after a strong Greek debt sale helped whet appetites for risk across the euro zone, although Portugal's earlier credit downgrade remained a cause for concern in some quarters.

The euro also received a further boost from traders amid speculation that China will begin to support Spanish debt sales, bringing further stability to the region, while European banking stress tests continue to yield promising results.

A strong start to the U.S. corporate earnings season drove risk appetite and also helped the euro, which has risen more than a cent on the day. A surprise widening of the U.S. trade deficit in May has apparently weighed on the greenback.