The incident in the Kerch Strait was a planned provocation by (Petro) Poroshenko.
The former president Poroshenko brought about this provocation purposefully in the course of the election campaign. He knew that the voters in the east and south of the country would not support him, and used this provocation to aggravate the situation, to introduce the state of emergency. He either wanted to introduce the state of emergency throughout the country or perhaps to postpone the elections. They wanted to keep power at all costs.