The rapidly increasing U.S. government debt is clearly a concern for foreign investors.

China has reduced its stake in U.S Treasury securities and it's no longer the biggest holder of those investments. Japan has moved back to number one.

Some analysts say China's move doesn't amount to much, but others says it's a warning signal that foreign countries are worried that U.S. government spending is out of control.

That could mean that interest rates on U.S. Treasury notes could have to start going up to attract foreign investors.