Tehran announced Monday that Russia had begun delivering its advanced S-300 air defense system to Iran in accordance with an agreement struck between the two countries earlier this year.

A defense ministry press release quoted by Iran’s semi-official Fars News dismissed “recent media reports” skeptical of the military deal, and confirmed the delivery of the S-300 surface-to-air missile system was underway.

“The recent remarks on the S-300 missile defense system delivery lack correctness and credibility and the executive stages for the delivery of the system are now being taken based on the previously signed contract,” the report said.

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There was no other confirmation that delivery had begun.

In August, the two countries announced that Russia would begin delivery of the system later this year, as the two countries talked of expanding military ties in the wake of a historic nuclear deal reached between Iran and six world powers in July.

Israel has long sought to block the sale to Iran of the S-300 system, which analysts say could impede a potential Israeli strike on Tehran’s nuclear facilities. Other officials have expressed concern that the systems could reach Syria and Hezbollah, diluting Israel’s regional air supremacy.

Last month, Prime Minister Benjamin Netanyahu met with Russian President Vladimir Putin in Moscow to discuss a mechanism to avoid military confrontations between the two countries in Syria.

During the meeting, Netanyahu told Putin that Iran and Syria have been arming Hezbollah with advanced weapons and missiles, thousands of which are directed at Israeli cities, and that Israel would continue to target arms transfers to the terrorist group positioned on Israel’s northern border.

Netanyahu said that he told Putin in “no uncertain terms” that Israel would not tolerate Tehran’s efforts to arm Israel’s enemies in the region, and that Jerusalem had taken and would continue to take action against any such attempts.

In response, Putin said that the Syrian army was too bogged down in its own civil war to deal with fighting against Israel, but told Netanayhu he understood Israeli concerns.

The S-300 is capable of tracking multiple planes at once and some versions have an interception range of 200 kilometers. It is considered to be one of the most sophisticated anti-aircraft weapons in the world.

Russia initially agreed to sell the advanced system to Iran in 2007 but then balked, saying at the time it was complying with a United Nations arms embargo.

Shortly after the Lausanne outline for the nuclear deal between P5+1 powers and Iran was signed in April, Russia announced it was lifting the ban on selling the advanced missile defense system to Iran, despite US and Israeli objections.

Moscow said at the time that the framework agreement permitted the delivery of the missiles without waiting for the removal of sanctions that were intended to deter Tehran from developing its nuclear program.

Jonathan Beck and Adiv Sterman contributed to this report.