Russia's Foreign Minister Sergei Lavrov did not say — as other Kremlin officials have — that technical reasons were to blame for not exporting the truck-mounted missile that can than hit aircraft up to 150 km (90 miles) away.
Lavrov's comments follow a spate of earlier signals from Moscow that Russia is hardening its position towards Iran's nuclear programme and preparing to back U.N. sanctions.
"There are questions that need to be settled before the contract can be executed," Lavrov said, when asked when Russia would sell the S-300 system.
"There are fundamental principles linked to the sale that we never, in accordance with our legislation, and according to our international obligations, take any actions that will lead to the destabilisation of certain regions," he said.
On February 19, a deputy Russian Foreign Minister said Russia intended fulfilling the contract.
"There is a contract to supply these systems to Iran, and we will fulfil it," Sergei Ryabkov told Interfax new agency in an interview.
"Delays (with deliveries) are linked to technical problems with adjusting these systems," he added.
The possible sale of the S-300s, which could protect Iran's nuclear facilities against air strikes, is an extremely sensitive issue in Russia's relations with Israel.
Israeli Prime Minister Benjamin Netanyahu visited Moscow last week to press the Kremlin to back tougher sanctions against Iran.
Lavrov said his comments did not refer only to the S-300 sale and hinted at the export by other countries of offensive weapons to Georgia.
"I never mentioned any political issues in the Middle East. I said there are certain principles we need to abide by when selling arms everywhere — Latin America, Middle East, the Caucasus region."
"We cannot sell weapons if that can lead to the destabilisation of the regions in question," Lavrov said.
(Reporting by Conor Sweeney; Editing by Michael Roddy)
