* International court extended Nicaragua sea border
* Experts say ruling is binding, withdrawal not retroactive
BOGOTA Nov 22 (Reuters) - Colombia is considering withdrawing from a treaty that forces the country to comply with an international court ruling that grants Nicaragua jurisdiction over Caribbean waters near a Colombian archipelago, the government said on Thursday.
The International Court of Justice this week ruled that a cluster of disputed small islands in the western Caribbean belonged to Colombia and not to Nicaragua, but drew a demarcation line in favor of Nicaragua in the nearby waters.
The court said the territorial waters extending out from the seven islets, which are nearer Nicaragua's coast than Colombia's, should not cut into Nicaragua's continental shelf. The ruling reduced the expanse of ocean belonging to Colombia.
"We should act quickly and study the possibility of withdrawing from the Bogota Pact," Foreign Minister Maria Angela Holguin told the Colombian Congress. She said she feared Nicaragua could file another complaint at the international court to further extend its sea borders.
The Bogota Pact is a treaty under which signatory countries agreed in 1948 to recognize ICJ rulings and to find peaceful solutions to their conflicts.
However, experts told Reuters that Colombia's withdrawal from the treaty would not have retroactive effect, and that it would still be obliged to comply with the ruling.
"It's too late to do that ... the country will not achieve anything because the ruling has already been issued," said Jose Gregorio Hernandez, former head of Colombia's Constitutional Court.
Menno Kamminga, professor of international law at Maastricht University in the Netherlands, said that if Colombia decides to withdraw from the court's jurisdiction, it will only affect future rulings.
"The ruling can't be repudiated, because both states agreed to the court's jurisdiction in advance," Kamminga said.
The decision, which is binding, increases the size of Nicaragua's continental shelf and economic exclusion zone in the Caribbean, which would give it access to underwater oil and gas deposits as well as fishing rights.
In 2007, the court, which is based in The Hague, ruled in a long-running dispute between the two countries that the three larger islands of San Andres, Providencia and Santa Catalina belonged to Colombia.
The ruling on Monday related to a further seven islets and the associated offshore rights surrounding them. The three larger islands have been controlled by Colombia since Nicaragua ceded them in a 1928 treaty.
Colombian President Juan Manuel Santos rejected the changes to the border, which effectively put some islands outside of the rest of the archipelago, saying the ruling had "omissions, mistakes, excesses, inconsistencies, that we can not accept".
The cluster of islands is more than 700 km (437 miles) from the Colombian coast, but only 200 km (125 miles) from Nicaragua.
Nicaraguan President Daniel Ortega welcomed the ruling as a recognition of his country's rights to fishing in the area and potential oil deposits. He criticized Santos for suggesting that Colombia would fight the court's ruling.