Decades after the Cold War, Russia and the US are continuing their chessboard game of weapons trading, says Siemon Wezeman from SIPRI, the influential Stockholm-based think-tank dealing with conflict and arms control.

DW: Has Moscow recently boosted its support to states such as Syria and Iran which are ruled by regimes traditionally hostile to America?

Yes, to Syria, to some extent. Russia, like the Soviet Union in the past, has always been the biggest supplier of weapons to Syria. Russia sees Syria as one of its last allies in the Middle East, so they tend to provide a bit more support, both with weapons, as well as military operations. Iran is another country where Russia has had long-term relations, but of course Iran is still under a partial UN arms embargo which has stopped some of the Russian supplies. Russia is definitely interested in Iran, supplying it, keeping it as a friend but not necessarily as an ally. But Iran also has the option to look to China as a weapons' source.

The sale of the advanced S-300 missile systems to Iran – was it motivated by profit or political reasons?

As usual, it is a mixture of both. It did provide the Russian industry with income, but it's also a political statement when you sell weapons. It may be that the Russians have cut their own fingers a bit in this, because the statement is, of course 'We support Iran.' This doesn't play very well with the West. This doesn't matter that much for Russia. But it also doesn't play well with Arab nations and the Russians have been trying to improve relations with Arab countries and sell them weapons. If you sell them to Iran, Arab countries say 'no, forget it.'

What was the US reaction to Russia selling weapons to Iran?

The US response to the weapons' sale to Iran was really simple. They said it was a bad thing because of the arms embargo, and the Russians said 'Well, we can still supply them because these weapons are not covered by the embargo.' Then the US said – 'If you think that way, we'll start listening more to our Arab allies.' So the US has said yes to a lot of demands for high-tech weapons from Saudi Arabia and the United Arab Emirates. It's not only because of the Russian S-300 delivery to Iran, but it plays a role.

And how did Washington respond to Russia supplying the Syrian regime?

Syria getting weapons – basically it's all for internal use, so it doesn't threaten anybody except the rebel forces. Of course that leads to Arab countries supplying weapons to rebels in Syria. And the Americans basically say to the Arab countries 'Go ahead, we are not going to interfere with that.'

The US and some other Western countries have a very clear idea whom exactly they want to supply in Syria – it's the liberal, Western-like rebel forces, certainly not the jihadists. Although sometimes you have no idea anymore who is who in Syria. We only know that weapons are going from Saudi Arabia to the Syrian rebels, including the moderate rebel forces, but some of it most likely disappears, goes to the jihadists. The way that this has been done and whether it was done on purpose by some elements of the Saudi government, is very unclear.

What about Eastern European countries that traditionally use Russian-made weapons? Is the Kremlin looking to get back in this market, especially in friendly counties like Serbia or Bulgaria?

Certainly with those countries that are not part of NATO, they are always looking to see if they can in any way weaken links with the West and improve links with Russia. Selling to NATO countries isn't really an option. There are sales, occasionally, for spare parts and bits and pieces and upgrades for Soviet equipment that is still being used in Bulgaria, for example. Bulgaria is planning to buy new engines for MiG-29s, because they still use those. Serbia, of course, is a bit different. It's not a NATO member, so the Russians look at it and say 'Well that's a place we can play with, let's see how far we can go with them.' From the Serbian side, it's the weapons they are familiar with, they fit within the structure and of course, they are cheap.

This week, Turkey announced it would soon take delivery of the first two US F-35 fighter jets. The plane is famously plagued by high costs and performance issues. Is buying it also a political decision, a friendly signal to the US?

Turkey is a NATO ally. They decided to buy it years ago - their plan is to have 116 F-35s. If the plane doesn't function as well as it should right now, it's still the only fifth-generation fighter plane there is. It's something that will work over the next 40 years, which is why they have bought it. Also, the Turks see themselves as a big power in the Middle East, and as a big power you have to have state-of-the-art weapons. International relations do play a role, and Turkey's ties with the US have been a bit strained in recent years. In telling the US that they are going to buy the F-35s, they should earn some extra credit in Washington.

In addition to arming their allies, both Moscow and Washington have been arming themselves. What specifically have they updated?

The Russian navy has certainly received a relatively strong input in the last few years. The army and the air force have also bought a lot of new equipment. It's the same in the US. All three branches get a good piece of the pie. They all have large modernization programs. I think the newest one is the nuclear forces, which are not as sensitive when it comes to modernization as other forces – a nuclear weapon will function whether it's a 20-30 years old missile or not. Now there are also moves in this area as well. The US side is looking into acquiring new missiles. Their current ones are getting a bit old and they need to renew them. On the Russian side there are also new nuclear submarines with nuclear weapons. Until 2014, some of the Russian ballistic missiles used Ukrainian spare parts but this has now stopped. A lot of these parts came from the Ukraine, so the Russians are in a bit of a hurry to modernize their land-based nuclear missile systems.

Siemon Wezeman is a senior researcher at the Stockholm International Peace Research Institute (SIPRI).