ANKARA, Turkey — One year after Turkey and Russia agreed to restore their badly strained relationship over Turkey's downing of a Russian Su-24 fighter jet due to an airspace violation, Ankara and Moscow say they are working on the final details of a defense deal speculated to be worth more than $2 billion. Some industry sources say the deal may be just the beginning of further Russian sales to Turkey, but analysts remain cautious about "incompatibilities."

In February, Turkish Defence Minister Fikri Isik said talks between Turkey and Russia for the potential acquisition of the Russian-made S-400 system "made quite [the] progress."

"The S-400 [system] looks like the closest option," Isik said.

The Russians came into the picture as Turkey was looking for a solution to its T-LORAMIDS program for the construction of the country's first long-range air and anti-missile defense system. 

Turkey in September 2013 selected a Chinese contender for the T-LORAMIDS contract for $3.44 billion. Under pressure from NATO and Western allies, Turkey later scrapped the deal and opened negotiations with U.S. (a partnership of Lockheed Martin and Raytheon) and European (Eurosam) contenders. As these talks progressed in theory, Turkey abruptly announced it was close to a Russian deal.

In March, Turkish President Recep Tayyip Erdogan and Russian President Vladimir Putin discussed the S-400 deal at a meeting in Moscow. And on June 1, Putin said: "We are ready to deliver these newest and most efficient systems. President Erdogan and our countries' militaries are aware of it."

The potentially looming S-400 deal could pave the way for the sale of further Russian systems to Turkey, some industry sources say. 

According to Burcin Girgin, general manager of Proterm, a Turkish agent for some of the systems distributed by the Russian conglomerate Rosoboronexport, offered as an example that Russian-made security systems could be integrated into the watchtowers of a planned 400-kilometer wall on Turkey's problematic border with Syria. Other Russian systems could also be used in Turkey's cross-border military incursion into northern Syria to fight Islamic State militants, Girgin said. 

Some Russian security systems could effectively be used in Turkey's asymmetrical fight against a number of militant organizations including ISIS and the Kurdistan Workers' Party. One particular Russian system, Girgin said, can detect handmade explosives at a distance of 30 meters and can be an asset in Turkey's fight against terror.

Another important, nonlethal system is a powerful beam projector that can be used against targets at a distance of 3.5 kilometers, causing the enemy temporary blindness for up to half an hour.

Turkey's state-controlled military electronics specialist Aselsan, the country's largest defense firm, is hopeful about a large-scale Russia-related program. In April, the company said it is seeking an "active role" in the future modernization work for 10,000 Russian-made Mi-series helicopters worldwide. Aselsan referred to that ambition as its "most important next goal." It said it has a particular interest in upgrading Mi-series helicopters in the Gulf and Central Asian countries.

Another industry source in Ankara said although Russia and Turkey can seek procurement deals in electronic systems, ammunition and missile technology, there are potential snags.

"Turkey wants to develop these systems indigenously, and I do not think Russia will wish to share its technology with a country that only a year and a half ago shot down its military aircraft and could in the future pose a security threat to its own interests in the Middle East," he said.

An Ankara-based expert on Turkish-Russian defense trade said the two countries have "completely different business mentalities." There is, he said, a striking incompatibility.

"But some longer-term cooperation, particularly in naval and land systems, can be possible, especially weapons systems to be installed into naval and land platforms," the expert said.

In agreeance with Girgin, the expert said some Russian-made gear, particularly what he called "peculiar items" to be used in asymmetrical warfare, can find a niche market in Turkey. "These would be high-tech anti-terror systems," he added.

Yet, he cautioned that the Turkish-Russian detente is too premature at the moment, and the two countries' diverging political priorities and goals in the Middle East — especially in Syria — can change the climate and make Russian systems simply unwanted in Turkey. "Any future significant Russian penetration into the Turkish market would be too much exposed to political risk," he said.