The chairman of the European Securities and Markets Authority (ESMA) said while there was no plan to extend a ban on short-selling financial stocks to other countries, such a move could not be ruled out.
ESMA Chairman Steven Maijoor told Reuters TV the curbs, brought in to rein in wild fluctuations in European stock values amid a flurry of rumours, would be in place for a while and would not be permanent.
"There are no concrete plans at this stage for other countries, but we cannot rule out that might change in the coming days and weeks and months," he said.
Belgium, France, Italy, and Spain banned short-selling of financial stocks after two days of drastic moves targeting European financial shares, with French bank Societe Generale undergoing the most brutal swings.
Maijoor said he was confident the ban would help bring confidence back to markets frazzled by Europe's longstanding debt crisis and the whirling rumours of ill-health in the French banking sector.
But market players assailed the ban as both too narrow - Austria, Britain, the Netherlands and Sweden have said they see no need for a ban - and too easy to circumvent by speculating on derivatives and other instruments.
Responding to that criticism, Maijoor invoked ESMA's limited mandate over national markets and urged European policymakers to move more quickly in pushing through EU-wide legislation on short-selling as quickly as possible.
The European Commission, the bloc's executive branch, echoed Maijoor's call, welcoming the four-country ban while insisting on the need for stronger EU-wide legislation.
Maijoor, whose office is based in Paris, referred to rumours on the solidity of France's AAA credit rating as one factor behind ESMA's decision to bring about a ban on short-selling, in addition to jitters about the debt crisis.
"All options were on the table" with regard to an extension of the ban or a widening of the instruments targeted, he said.