The euro can ultimately only succeed if EU countries agree to a political union, the former head of the US Federal Reserve, Alan Greenspan, said in an interview.

The single currency "can only be saved via a political union," Greenspan told Germany's Welt am Sonntag newspaper.

"I don't believe that a common economic and currency area can function in the long term if it is made up of 17 countries with 17 different social systems," Greenspan said in comments reproduced in German.

"The eurozone needs a complete political union, comprising either all member states or a core Europe. That is the only way the eurozone isn't going to break up," Greenspan told the newspaper.

Asked whether the global financial crisis that erupted in 2008 could happen again, Greenspan replied: "Absolutely. No question."

During the economic crisis, he said, "the interest rates on government bonds of the southern states soared, while they remained low and stable for Germany and some other countries such as the Netherlands, Austria and Finland."

"The system does not work very well. There is no balance," he said.

Greenspan, 87, was chairman of the Federal Reserve between 1987 and 2006.