KIEV (Reuters) - Kiev will tighten control over travel by Russian citizens to Ukraine, according to a decree signed by President Petro Poroshenko on Wednesday, a further move by the authorities to distance Ukraine from its neighbor and one-time ally.

Russians and Ukrainians have traveled freely between each other’s countries since the collapse of the Soviet Union in 1991, but Kiev has sought to implement a stricter regime in the wake of Russia’s annexation of Crimea in 2014 and role in the separatist conflict in eastern Ukraine.

Poroshenko has now signed a decree that will require Russians and citizens of certain other countries to notify the Ukrainian authorities in advance about their reason for traveling to Ukraine.

This is aimed at “safeguarding state security and neutralizing threats in the areas of migrations and citizenship”, Poroshenko’s administration said in a statement.

The decree relates to “foreigners, particularly citizens of the Russian Federation and individuals without citizenship, who come from migration risk countries”, the statement said, without giving further details on which countries this concerned.

According to the Ukrainian state border service, there were 1.5 million trips by Russians to Ukraine in 2017.

The government has a month to implement the decision, but it is not clear when the new rule will come into force.

At the start of 2018, Ukraine introduced biometric controls for Russians entering the country, but the government has stopped short of imposing a formal visa regime.

Relations between Kiev and Moscow are at an all-time low after Russia annexed the Crimean peninsula and backed pro-Russian separatists in Ukraine’s eastern Donbass region in an ongoing conflict that has killed over 10,000 people.