Russian authorities have cited a series of incidents in eastern Ukraine to justify military action.
In his speech on Monday, Vladimir Putin said that Ukrainian authorities are "not interested in a peaceful solution."
"On the contrary, they are trying to mount a blitzkrieg in Donbas," he said.
But the US has warned that Russia is faking provocative acts – so-called “provocations” incidents.false flag“, which are staged to appear to come from one side in a conflict – in order to create a pretext for military action.
So what happened in eastern Ukraine and what do we know about it?
What is a false flag attack?
Alleged "sabotage" by separatists
The Organization for Security and Cooperation in Europe has tracked thousands of ceasefire violations in recent days.
But there is a growing body of evidence showing that online rumors have misinterpreted some attacks and that some events may even have been staged by the Russian side itself.
For example, on Friday, a video circulated on a Telegram channel run by Russian-backed separatists. The material purports to depict a clash between an “enemy sabotage group” and pro-Russian forces in eastern Ukraine.
The post featured a video of pro-Ukrainian militants trying to blow up a chlorine tank in the Donbas area controlled by pro-Russian separatists.
"Ukrainian armed formations are deliberately trying to sow fear and panic among the civilian population," the post says. "The above facts are direct confirmation of the Ukrainian side's preparations to start hostilities."
The video was later picked up by pro-separatist and Russian news agencies.
But open-source investigators on social media pointed out several inconsistencies that indicated the video was shot at an earlier date and had been manipulated.
While inspecting video metadata – which can be used to see when a file was created or modified – investigators found that the video's creation date was February 8 – ten days before it was posted.
The video also appears to have dubbed audio, taken from a YouTube video posted in 2010 at a military training ground in Finland. It seems highly unlikely that this video shows what the separatists claim it does.
The full article i BBC