The Russian Foreign Ministry on Saturday asked a Ukrainian diplomat to leave the country after he was caught red-handed receiving classified information from a Russian citizen.

The Russian foreign ministry said later Saturday that it had summoned Ukraine's charge d'affaires Vasyl Pokotylo and told him that the Ukrainian diplomat had 72 hours to leave the country "beginning April 19".

"The Russian side pointed to the inadmissibility of such kind of activity," the foreign ministry said in a statement. 

The Ukrainian diplomat detained in St. Petersburg, was held for several hours, and he was now back at the country's consulate, said Ukraine's foreign ministry on Saturday. 

Russian news agency TASS reported on Saturday that Russia's Federal Security Service (FSB) detained a Ukrainian diplomat in St. Petersburg a day earlier, accusing him of obtaining classified information from a Russian national.

"On April 16, the Federal Security Service apprehended Ukrainian diplomat - consul of the Ukrainian General Consulate in St. Petersburg Alexander Sosonyuk red-handed upon receiving classified data from the databases of Russian law-enforcement agencies and the FSB," the press office said in a statement.

"This activity is incompatible with the status of a diplomatic employee and is hostile to the Russian Federation. The foreign diplomat will be dealt with in accordance with international law," the FSB said.

Ukraine's foreign ministry said the Ukrainian side will soon decide how to respond to this provocation.

The case was the latest flare-up of tensions between the two neighboring countries as bilateral ties soured amid a build-up of Russian troops along the border and clashes in eastern Ukraine between the army and separatists.

(With input from Reuters)

(Cover: Ukraine's President Volodymyr Zelenskiy visits positions of armed forces near the frontline with separatists during his working trip in Donbass region, Ukraine, April 8, 2021. /Reuters)