Quotes from blogs concerning this event from godlikeproductions blog site:
I don't know if are Putin words (the "US an EU look at this" part) or not, but this russian jurno just said this:
http://www.godlikeproductions.com/forum1/message2868789/pg332

Putin: 2 Russian military were killed, US an EU look at this, we will answer

marqs ‏@MarQs__ 17 s

The Crimean Parliament has considered the preparation of terrorist acts by Kiev as an 'declaration of war'
Reports of a 'Russian military convoy' passed through Pereval'sk towards #Debaltseve some while ago:
[link to twitter.com (secure)]

[link to translate.yandex.ru (secure)]

Re: UKRAINE/RUSSIA: Breaking: Crimean Council: subversive group attack is like a declaration of war!!!p.331

So, just to recap

1) Putin just sent a giant f##k you to Normandy Four format
2) Putin said Russia will answer the death of the two soldiers
3) Putin says Ukraine government is using terror tactics (this can probably be useful for a legal basis of the "response", would be "fighting terrorism" instead of "war")
2) Crimean Parliament compare what happened to a "declaration of war"
3) Ukraine deny it has something to do with this
4) A lot of russian activity in Crimea and along the border in the last days/weeks
5) Olympics ongoing

Russia needs to take Mariupol and this is why I've always felt it's just a matter of time before they move in...
Google translate shitty translation, happened less than an hour ago, there are a lot of details so i think its not a bullshit:

.. "Kharkiv region Shootout near s.Goptovka (. Transition Kharkiv - Belgorod region) Gunfight in the village on the border with Belgorod began at 22:20 Reported intensive gunfire Svetlodarsk Lugano-Logvinova: small arms, mortars + + BMP... . with two positions APU in Svetlodarsk made bombardment of ACS towards Uglegorsk from the Svetlodarsk also under fire in the direction of Debaltsevo Donetsk Party warheads and Avdiivka industrial zone:... used artillery route Svetlodarsk-Debaltsevo and zelenka west slopes under fire, are fighting with. mortars and Arta. Mariupol. with direction Talakovki-Gnutova and Sartana from several positions alternately APU for several hours firing on Kominternovo and the surrounding area from the heavy artillery. "

.. From the residents: "Donetsk Yasinovataya a terrible storm of self-propelled guns and 120 mm Sound now such as from a MRL can not understand what is happening in the area of the airport, Spartacus falls heavy Very loud Makiyivka - Gvardeyka, Butovka loud signalization on the machines..... worked gromkovato nursing, nuclear warheads East side Gremio Trudovskoy -... fight Petrovka Amstor- Starovihaylovka- Abakumov loud Kiev RIC-Putilovka grohochat "....

DWS Intel ‏@DWSIntel · 8m8 minutes ago

More heavy transports into Crimea from Moscow.

[link to pbs.twimg.com (secure)]
Putin calls "attempt to commit terrorist attack in Crimea" a "very dangerous game"