Algeria, Egypt, Iraq, Morocco, Qatar, Saudi Arabia and Vietnam were among the countries that had already engaged in talks on buying the Russian missile systems, the CNBC broadcaster reported on Wednesday.
Washington expected that several countries would yield to the US pressure and abandon their plans to purchase the Russian equipment, the outlet added.
"Many of these countries do not want to wait for US regulatory hurdles … The S-400 has less export restrictions and the Kremlin is willing to expedite sales by skipping over any regulatory hurdles. It's like buying it off the shelf," one of the sources told the broadcaster.
Another source noted that S-400 had been more powerful, in terms of capability, than the US most capable Terminal High Altitude Area Defense (THAAD) system.
"No other US system can match the S-400's ability to protect large swathes of airspace at such long ranges," the source, who was not authorized to speak publicly, said.
Sanctions over the purchase of the Russian military equipment could be triggered under the US Countering America's Adversaries Through Sanctions Act, which came into force in 2017 and is set to punish Moscow for it alleged meddling in the US 2016 presidential election, something vehemently denied by Russia.
Apart from China, India and Turkey have also reached agreements on the purchases of the missile systems from Russia. Turkey’s plans have, particularly, been a point of concern for the United States since Ankara is Washington’s NATO ally.
The Saudi authorities have also been openly engaged in talks with Russia on the missile system purchase.
S-400 is the next-generation mobile missile system which can carry three different types of missiles capable of destroying a variety of aerial targets at a short-to-extremely-long range, from reconnaissance aircraft to ballistic missiles.