Citizens of the RF (civilian "protesters" and troops) are in Donbas. Ukrainian SBU was getting tons of them. What additional proof of Russian involvement can there be? For Putin to formally admit it? He won't. If you recall, he didn't admit to Russian troops taking over Crimea.
Putin doesn't have to admit anything, and neither does the EU or US.....it's a war now of many moving parts, it doesn't have to be called one to make it so. My gosh you have people dying, fires, violence, military of ‘all kinds’ running round about.
Further You have people doing back door negotiating with numerous city folk...and this by who? Ukraine and those within the cities of dispute...and this with the USA guiding the Kiev Gov.
Imo all the nation Leaders are assisting Ukrainians to handle this because Ukraine certainly can't do this alone....their history reveals this. In the end it will not be Ukraine who determines this outcome....they lost that the minute they deposed an elected Pres. by violent force.
Only when they have an election will this be determined as Ukraine might desire and it frankly doesn't look like they'll be having any May election at the rate they are going....this would be to who;s advantage should they be delayed?....of course those currently sitting in the seat of power.