A U.N. spokesman said an extension had been granted until mid-June following closed-door talks in Geneva. This would allow the four states to fill in gaps in information that was "unclear and incomplete," he told a briefing.

"The CITES reprieve means the spring fishing season, the biggest of the year, will go forward," said Caviar Emptor, a coalition of three groups seeking to protect endangered Caspian Sea sturgeon.

The spring season usually accounts for 70 to 80 percent of the annual catch, they added.

The global caviar market has placed a premium on Caspian sturgeon, prompting over-fishing and illegal trade that have driven the ancient species to the brink of extinction, according to the groups: the Natural Resources Defense Council, Seaweb, and the University of Miami's Pew Institute for Ocean Science.

In a statement, they said the four Caspian states had taken no significant steps to collaborate in management of sturgeon, to set up a long-term program to survey the sturgeon population or to combat illegal trade.

Iran, the fifth country bordering the Caspian Sea, is also part of the "Paris Agreement" of June 2001, but is deemed to have good fisheries management, according to the U.N. spokesman.