Israel warned the United States in recent days that Russia plans to sell advanced ground-to-air missile systems to Syria despite Western pressure on Moscow to hold off on such a move, the Wall Street Journal reported on Wednesday.
The newspaper said U.S. officials had confirmed they were analyzing the Israeli reports but would not comment on whether they believed the sale of S-300 missile batteries was near.
No comment was immediately available from officials at the Pentagon or U.S. State Department.
The government of Syrian President Bashar al-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 125 miles (200 miles), with an initial shipment expected in the next three months.
While the effectiveness of Syria's aging air force is unclear, most experts believe that its air-defense missile system, which was upgraded after a 2007 Israeli strike on a suspected nuclear site, remains quite potent.