Iran has displayed parts of its new Russian-made air defence system during its Army Day celebrations.
Pictures released by the semi-official ISNA news agency showed S-300 missile tubes and radar equipment during a military parade in southern Tehran.
Iran insists the system is necessary to defend itself, but the US and Israel have criticised the sale.
The controversial contract got the go-ahead after last year’s deal to lift international sanctions on Iran.
Six world powers led by the US agreed in July to lift the sanctions which had locked down much of Iran’s economy for years, in exchange for limits on Tehran’s nuclear programme.
The missile parts went on display as President Hassan Rouhani pledged to defend Muslim countries against “terrorism and Israel” while insisting that his country’s neighbours should not feel threatened.
Iran ‘receiving Russian missile system’
Speaking during the National Army Day parade he praised Iran’s role in assisting Syrian and Iraqi forces curtail advances made by the so-called Islamic State group.
“If tomorrow your capitals face danger from terrorism or Zionism, the power that will give you a positive answer is the Islamic Republic of Iran,” the president said.
The $800m (£562m) missile contract, signed in 2007, was frozen by Russia in 2010 because of international sanctions against Iran. President Vladimir Putin unfroze it a year ago.
The S-300, made by Rostec, can be used against multiple targets including jets, or to shoot down other missiles.
The S-300V4 variant, delivered to the Russian armed forces in 2014, can shoot down any medium-range missile in the world today, flies at five times the speed of sound and has a range of 400km (249 miles), Russia’s Tass news agency reported recently.