Health Minister Maksym Stepanov says that the government has mandated a negative PCR test for COVID-19 as a prerequisite for entering Ukraine.
All foreigners will need to present a negative covid test (taken within 72 hours before arrival) to enter Ukraine. It does not matter which country you come from.
As of now, it seems that this rule even applies to people who were vaccinated outside of Ukraine.
These new regulations came into effect on March 22nd.