An Iranian opposition group claimed Saturday that Iran's capture of 15 British sailors and marines was planned in advance and carried out in retaliation for U.N. sanctions imposed against Tehran.

The National Council of Resistance of Iran — the political wing of the Iranian MEK opposition group which is listed as a terrorist group by Britain, the U.S. and the European Union — said the British crew's capture was planned in advance, but offered no evidence to support the claims.

Hossein Abedini, a member of the council's foreign affairs committee, claimed the group had obtained information from sources within Iran's Islamic Revolutionary Guard and had passed details to the British government. He did not provide any evidence or give further details.

Britain's Foreign Office said it could not comment on Abedini's allegation, or say if it had evidence the operation was pre-planned. A spokeswoman said the MEK was a banned organization under British anti-terrorism laws — meaning the government had no dealings with the group.

Abedini told a London press conference that an Iranian Revolutionary Guard naval garrison had been on alert from the night before the kidnapping, to prepare for the operation.

Mohammad Mohaddessin, who handles foreign affairs for the council, said in a statement that Iran's supreme leader, Ayatollah Ali Khamenei, had ordered the detention of the Britons in the hope of pressuring the British government over a threat to toughen U.N. sanctions.

The U.N. Security Council voted to toughen measures against Iran on March. 24, to force Tehran to halt a uranium enrichment program, which the U.S. and allies claim is a cover for the illicit development of nuclear weapons. Tehran insists it is engaged in producing civilian nuclear power.

The security council vote came a day after the British crew were seized in the Persian Gulf following the routine boarding of a merchant ship.

Britain insists the crew were in Iraqi waters when seized. Tehran says they were in Iranian waters.

"You can see that the clerical regime had in a premeditated act arrested British sailors in order to win concessions from the international community and divert attention from its nuclear project," Abedini said. "Claims that the sailors were arrested in Iranian territorial waters are baseless."