A ban on short-selling financial stocks in four European countries including France takes effect on Friday, a coordinated attempt to restore confidence in markets hit by rumours and higher borrowing costs.

France, Italy, Spain and Belgium imposed the ban, which will vary in detail depending on the country, the European Securities and Markets Authority (EMSA) said in a statement late on Thursday.

European markets have repeatedly moved on rumours about the health and funding needs of indebted euro zone governments, and more recently on some of its major banks, which have sent shares tumbling.

The DJ Stoxx index of European banking stocks has fallen 37 percent from a peak in February and touched a 28-month low on Thursday. The index is down 17 percent in August alone.

Financial industry participants and academics questioned the value of the short-selling bans.

"It's one of those things that politicians grasp for when they have no other tools left in their arsenal," said James Angel, an associate professor specializing in financial market regulation at Georgetown University's McDonough School of Business in Washington DC.

"All it really does is kick sand in the ears of the market and signals to the world that the leaders are clueless as to what's going on."

Stock futures pointed to a firmer open for European markets on Friday, with France's CAC 40 futures up 0.4 percent, lagging a 1 percent gain for the pan-European Eurostoxx 50 futures.

European regulators had previously played down the idea of a blanket ban on short-selling, through which an investor borrows shares and sells them on the expectation their price will fall and they can be bought back at a lower price.

EMSA said short-selling combined with rumour-mongering created a strategy that was "clearly abusive."

"Today some authorities have decided to impose or extend existing short-selling bans in their respective countries," it said. "They have done so either to restrict the benefits that can be achieved from spreading false rumours or to achieve a regulatory level playing field."

France will ban short selling on 11 financial stocks for 15 days, Spain will protect 16 stocks for 15 days, while Belgium will ban short selling of four financial stocks for an indefinite period. Details of the Italian ban were not immediately clear.

Banks on the list included France's BNP Paribas and Societe Generale , and Spain's Santander and BBVA .

French Finance Minister Francois Baroin said he welcomed the ban, while adding the country's banks were among the world's safest.  - Reuters