Short-selling of certain stocks is now forbidden in France, Italy, Spain, and Belgium. The ban on short-selling comes as concerns about Europe's debt worsen.
Markets had rebounded by late in the day, but they're still fragile, economists say. Leaders of France and Germany have announced plans to meet next week to discuss Europe's financial troubles.
But that hasn't dampened calls from critics who worry that centralizing European Union fiscal policy would impinge on national sovereignty – and possibly even worsen the crisis.
In the globally connected economy, financial pain in either Europe or the US has worldwide ripples.
Investors in Europe have set their sights on Italy, speculating that if a Greek bailout isn't approved and Athens defaults on its government debt, Italy is next.
With high debt and falling stocks, Italy appears to be the next European economy on the brink. Investors and European officials are now sounding alarm bells.
American exposure to the Greece crisis is high in certain areas. Half the assets in the 10 biggest money market funds are invested in European banks, which hold a lot of Greece's debt.
Nearly half of US mutual fund assets are invested in European banks, some of which face big losses in case of a Greek default. Banks could see their ratings downgraded after a Greek default.
Stock markets in Asia, Europe fall sharply after US stock markets plunge and Greek debt worries rise. Futures point to rebound in the US.