Russia may start the delivery of its S-400 air defense system to Turkey as early as within the next two years, Undersecretary for Defense Industries İsmail Demir has said.

Demir on Monday said: "I would not give a concrete date, as negotiations to minimize the delivery time are currently underway. But, we can say that the delivery will start in a minimum of two years."

Earlier on Sept. 11, President Recep Tayyip Erdoğan announced that the down payment for the S-400 has already been made to Russia. Demir also touched upon the contract bidding process to mass produce Turkey's latest main battle tank Altay. He said that bidding was due in two months, as the members of the defense industry waited eagerly.

Some European countries have expressed their concerns over Turkey's purchase of the S-400, claiming that it was incompatible with NATO system.

Turkey, however, is determined to purchase the Russian system. Turkish authorities have said that the purchase was needed to address the country's security concerns as an independent state.

With the addition of the air defense system, Turkey looks to block threats in the region, while Ankara has also demanded transfer of technology in order to develop its own missile defense system.

Turkey's need for an air missile defense system was exposed with the start of the civil war in Syria. The country has a sizeable ballistic missile stockpile able to strike a large portion of Turkey's territory.

Turkish officials were concerned that the missiles could be used by the Assad regime in case of a unilateral military conflict or an international military intervention, while the possibility of the missiles falling into the hands of a terrorist group posed a greater danger.

The country had to rely on Patriot batteries provided by its NATO allies Germany, the Netherlands and Spain during the conflict. They were withdrawn in 2015.

Turkey faced similar worries during the Iran-Iraq War and the First and Second Gulf Wars due to the ballistic missiles possessed by those countries.

In recent years, Turkey has sought to build its domestic defense industry to reduce reliance on foreign suppliers.

The S-400 is Russia's most advanced long-range anti-aircraft missile system and can carry three types of missiles capable of destroying targets including ballistic and cruise missiles.

It can track and engage up to 300 targets at the same time and has an altitude ceiling of 27 kilometers.