"A new act of provocation." That is what the Syrian government said about Turkey wanting to deploy Patriot missiles along the border between the two countries.
Turkey and Syria share a 900km border that Turkey says needs protecting in order to stop the conflict inside Syria from spreading.
"Russia is very sensitive when some missiles are deployed not only in Turkey, but wherever it is close to its strategic interest areas. Russia is extremely sensitive over that and it believes there is no absolute security so if someone says something about its own security then probably it will be at the expense of Russia's security."
- Sergei Strokan, a political analyst
The relationship between the one-time allies has gone from bad to worse since the uprising to oust Bashar al-Assad, the Syrian president, began almost two years ago.
Damascus has long accused Ankara of harbouring, financing and arming rebels fighting to oust al-Assad. Russia agrees with Syria and is warning that the surface-to-air missiles could lead to a regional crisis.
Sergei Lavrov, Russia's foreign minister, said: "Any build-up of weapons creates threats and risks. Any provocation can cause a very serious armed conflict. We would like to avoid it by all means. We are perfectly aware of Turkey's concern over the security on its border."
But Anders Fogh Rasmussen, the head of NATO, reassured Moscow that Turkey's decision was purely to protect its own territory: "The Turkish government stressed that the deployment will be defensive only, and that it will in no way support a no-fly zone or any offensive operation .... The security of the alliance is indivisible. NATO is fully committed to deterring against any threats and defending Turkey's territorial integrity."
To discuss this, Inside Syria, with presenter David Foster, is joined by guests: Shashank Joshi, an associate fellow at the Royal United Services Institute; Fadi Hakura, a specialist on Turkey from Chatham House; and Sergei Strokan, a political analyst and columnist and host of the current affairs show Red Line.
"I think that Washington, in particular, does not want a no-fly zone over Syria. Washington and Europe are not keen to get militarily involved in the Syrian quagmire. Therefore Turkey's repeated wishes to impose a no-fly zone over Syrian airspace has fallen on deaf ears and I don't think that this potential deployment of the Patriot missiles is part and parcel of enforcing a no-fly zone. I think it reflects a frustration in Ankara that there hasn't been a more robust and muscular reaction to the Assad regime from the United States and Europe."
Fadi Hakura, Chatham House