(JTA) — Russia will not sell the S-300 advanced air defense system to Syria, Russian Foreign Minister Sergei Lavrov has said.

Lavrov’s statement, published by the Itar-Tass news agency on May 10, came in reaction to a publication on Wednesday by The Wall Street Journal, that Israel had informed the United States a deal is imminent to sell the advanced ground-to-air missiles. Possession of S-300 missiles would significantly boost Syria’s ability to stave off intervention in the conflict, the daily reported.

Lavrov said Russia would fulfill contracts it has already concluded with Damascus but that this did not include sales of the S-300 system.

On Thursday, U.S. Secretary of State John Kerry said the United States does not want Russia to sell weapons to Syria and has opposed transfers of missile systems to the country in the past because of the threat to Israel.

“I think we have made it crystal clear we would prefer that Russia was not supplying assistance,” Kerry said at a news conference after meeting Italian Foreign Minister Emma Bonino.

The government of Syrian President Bashar Assad has been seeking to purchase the advanced S-300 missile batteries, which can intercept both manned aircraft and guided missiles, from Moscow for many years.

Western nations have repeatedly urged Russia to block the sale, which they argue could complicate any international intervention in Syria’s escalating civil war.

The Journal said the information provided to Washington by Israel showed that Syria has been making payments on a 2010 agreement with Moscow to buy four batteries for $900 million, including a payment made this year through Russia’s foreign-development bank, known as the VEB.

The paper said the package included six launchers and 144 operational missiles, each with a range of 200 miles, with an initial shipment expected in the next three months.