As more information comes out, it looks like it was a recce mission that took off from central Turkey, flew to Cyprus, the turned east and established an orbit in international waters off the coast as -Pikey put together. It must have been tracked for a good while and very accurately because (speculatively) as soon as it strayed just about a kilometer into Syrian airspace, it was immediately and decisively engaged. One thing I can say, things are tense in the region tonight, especially with Turkey talking about an appropriate response. This is just the type of incident that sparks wars.
Edit: Here's more on the Russian facility which what I thought to be a prize base lol: http://www.nytimes.com/2012/06/19/world/europe/russian-warships-said-to-be-going-to-naval-base-in-syria.html.