The first tranche of Russian-built S-300 long-range surface-to-air missile systems are en route to the Iranian military, according to senior officials in Tehran.

The weapons transited to Iran via the Caspian Sea arriving this week, the country's Foreign Ministry spokesman Jaberi Ansari said Monday.

"We had already announced that despite several times of change in time of delivery, the deal is on its path of implementation and today I should announce that the first phase of the agreement is implemented and the process will continue," he said according to state-run Mehr News Agency.

The weapons were part of an $800 million deal between Moscow and Tehran to provide five S-300PMU-1 missile system battalions, known by the NATO designation SA-20 Gargoyle, consisting of 40 launchers, to the Iranian Revolutionary Guard Corps.

Both countries had agreed to a deal for Russia to sell five battalions of S-300 systems in 2007, but former Russian president Dmitry Medvedev canceled the deal after the United Nations-imposed sanctions were levied against Tehran in 2010.

"There are no problematic issues in this sphere and the contract has been concluded," Russian Deputy Prime Minister Dmitry Rogozin said of the deal on Friday, Russian news agency Tass reported.