A piecemeal ban on short-selling of financial stocks highlighted flaws in euro zone policy and investors said relief for bank stocks would be temporary in the absence of co-ordinated action by Europe's governments.
France, Italy, Spain and Belgium imposed the ban, under which details varied according to country -- while Britain, the Netherlands and Austria said they saw no need for action and Germany remained silent.
It's naive to think that this in some way helps things, said Dipesh Patel, head of European equities at Espirito Santo Investment Bank.
The worry now is that this is a last-ditch attempt to keep stocks up against investor opinion.
European markets have swung wildly this week on rumors 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.
On Friday morning the STOXX Europe 600 banking index yo-yoed, then crept steadily higher. By 4:49 a.m. EDT it showed a 2.2 percent gain, helping the broader market to advance 3.8 percent.
French banks, at the center of much of the market's attention and included in the ban on short-selling, were up: Societe Generale rose 1.2 percent, BNP Paribas added 1.4 percent and Credit Agricole gained 0.3 percent.
The banking index has fallen 36 percent from a peak in February and is down some 17 percent in August alone.
Short-selling is the process 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.
However, market players said the ban did not tackle the root causes of investors' concerns -- joined-up, long-term fiscal policy in the euro zone - and pointed out that nervous mutual funds were currently behind the sell-off.
A crackdown on speculative short-selling is unlikely to arrest moves from institutional investors who have decided they have little stomach for big holdings in banks and indebted governments who might call on them again for emergency capital.
Data from various regulators of late have shown there is no short-selling activity out of the norm, said Davide Burani, financial analyst at Italian fund manager Horatius.
Investors are selling in Italy from fear. Italian banks are holding around 200 billion euros of Italian bonds.
Alessandro Frigerio, fund manager at Milan's RMJ Sgr said the ban could work if, combined with proposals from Tuesday's meeting of French President Nicholas Sarkozy and German Chancellor Angela Merkel, it were to give the idea that there could be a rescue for the euro zone and a rebound in the market
The European Securities and Markets Authority (ESMA) said short-selling combined with rumor-mongering created a strategy that was clearly abusive.
Some authorities have decided to impose or extend existing short-selling bans in their respective countries, it said late on Thursday. They have done so either to restrict the benefits that can be achieved from spreading false rumors or to achieve a regulatory level playing field.
France banned short selling on 11 financial stocks for 15 days, Spain said it would protect 16 stocks for 15 days, Belgium banned short selling of four financial stocks for an indefinite period and Italy said its ban covered 29 companies in the banking and insurance sector.
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 and added the country's banks were among the world's safest.
This week's market turmoil focused on speculation about French banks, which are heavily exposed to European countries at the center of the region's debt crisis. Societe Generale, France's No. 2 lender, has especially been in the eye of the storm.
Those rumors sent shock waves through credit markets, pushing interbank borrowing rates higher and triggering a 3-month high of 4 billion euros in emergency overnight borrowing from the European Central Bank.
But French 10-year bond yields dipped below three percent on Friday for the first time since November showing demand for the country's debt remained intact despite banking sector concerns.
The European assault mirrors one by the U.S. Securities and Exchange Commission on September 19, 2008, four days after Lehman Brothers collapsed, to temporarily ban short selling in 799 banks and other financial institutions.
Britain imposed a similar prohibition at that time.
The U.S. move was of questionable value, according to several academic studies. While share borrowing fell during the three-week ban, financial stocks continued to plummet.
In 2008 we already saw that such a measure doesn't work..its a temporary patching up measure for a problem that needs still be resolved, said IG Markets strategist Soledad Pellon in Madrid.
(Writing by Sophie Walker; Additional reporting by Sarah Young, Sinead Cruise and Laurence Fletcher in London, Stephen Jewkes in Milan, Judy Simpson in Madrid; Editing by Alexander Smith)