Mike Pompeo
Mike PompeoReuters

US Secretary of State Mike Pompeo on Wednesday called Russia's delivery of the S-300 surface-to-air missile system to Syria a "serious escalation".

“I’m certainly not going to comment on our intention on how we will address that, but my comments before were true. Having the Russians deliver the S-300 into Syria presents greater risk to all of those in the affected areas and to stability in the Middle East. We consider this a very serious escalation,” Pompeo said in remarks to the media.

His comments came a day after Russian Defense Minister Sergei Shoigu said that the delivery of the system to Syria had been completed and that work on preparation and training of the crews will be completed by October 20.

The missile system, originally developed by the Soviet military, but since modernized and available in several versions with significantly different capabilities, fires missiles from trucks and is designed to shoot down military aircraft and short and medium-range ballistic missiles.

On Tuesday, State Department spokeswoman Heather Nauert said that, while she could not confirm that the report about the delivery of the missile system to Syria, the move would be “a serious escalation in concerns and issues going on in Syria.”

Russia announced last week it would upgrade Syria’s anti-air defense network and send the S-300 system there, following the downing of a Russian military aircraft in Syrian airspace.

On Friday, Russian Foreign Minister Sergei Lavrov confirmed that delivery of the advanced missile system had begun.

Kan News reported on Saturday that Russia received $1 billion from Syria in payment for the S-300.

Israel has made repeated efforts to persuade Moscow not to sell the S-300s to Syria, as it fears this would hinder its aerial capabilities against arms shipments to the Hezbollah terrorist group.