Apparently it will soon be a lot harder for the U.S. or Israel to militarily intervene to stop Iran from developing nuclear weapons. The Iranian defense minister announced on Tuesday that Iran is planning to finalize a contract with Russia as early as next week to purchase four advanced S-300 surface-to-air missile systems.

Russia, Iran Finalizing Deal For Advanced S-300 Anti-Aircraft Missiles

This is not a new development, as Russian state arms producer Almaz-Antey noted earlier this summer it was planning to supply Iran with an upgraded version of the S-300, which is a highly-effective anti-aircraft system, after a final agreement was reached. However, it appers the size of the order has been increased from three systems to four systems.

According to the Iranian Fars news agency, Defense Minister Hossein Dehghan said: “The text of the contract is ready and our friends will go to Russia next week to sign the contract.”

More on Russia selling S-300 Missiles to Iran

Tuesday’s announcement was just one day following Iran’s Foreign Minister Mohammad Javad Zarif visit to Moscow, ostensibly to discuss the war in Syria.

Dehghan noted that while Iran had originally planned to acquire three “battalions” of S-300 launchers from Russia, it had decided to go ahead and boost the order to four.

Pieter Wezeman from Stockholm International Peace Research Institute suggested that each battalion would probably be an independent unit including a radar system, control system, and an unknown (double-digit) number of launchers.

“With four battalions, they should be able to deploy missile systems in four different locations,” Wezeman commented.

Although almost 40 years old now, the upgraded Russian S-300 system can engage multiple aircraft and ballistic missiles at ranges of 300 km (186 miles) away.

Also of interest, Dehghan mentioned that Iran was negotiating to to buy fighter aircraft. Military analysts say this is an effort by Iran to upgrade its aging fleet of mostly U.S.-made fighters with very few spare parts and no upgrades.

Iran nuclear deal facing tough road in U.S. Congress

Despite a major push by President Obama, Congressional approval of the recently signed Iran nuclear deal remains uncertain. Republican Senator Jeff Flake came out in opposition to the deal over the weekend, scuttling any hopes of bipartisan agreement. Democrats who have said they will support the deal include Senators Kirsten Gillibrand of New York, Tim Kaine of Virginia and Dianne Feinstein of California.

However, the deal is now nearly unanimously opposed by Republicans and by a number of prominent Democrats, including the Democratic leader Charles Schumer of New York.

The Iran nuclear agreement has seen dogged opposition from the government of Israel and many Jewish-American groups. These critics say the deal in effect rewards poor Iran’s behavior.

The U.S. Congress will vote on a resolution disapproving of the agreement in September. The White House has promised a veto if the resolution passes. If Obama’s veto is sustained, the White House can go ahead and implement the agreement without the support of congress.

Opponents to the deal would need two-thirds majorities in both houses of Congress to override the president’s veto (ie, 44 House Democrats and 13 Senate Democrats would have to vote to overide).

The dozen plus Republicans running for president have taken pot shots at the Iran nuclear deal and promised to make every effort to undo it.