Russia says Sosoniuk was detained for reportedly trying to obtain classified information.
Russia’s FSB security service briefly detained a Ukrainian diplomat in St Petersburg, Ukraine’s foreign ministry said on Saturday, in the latest flare-up of tensions between the neighbouring countries.
Interfax news agency earlier reported citing the FSB that Oleksandr Sosoniuk was taken into custody when he tried to obtain classified information from Russian law enforcement databases during a meeting with a Russian citizen.
“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 was quoted as saying, adding that Sosoniuk was detained on Friday.
Ukraine’s foreign ministry said Sosoniuk was held for several hours but was now back at the country’s consulate in St Petersburg.
“The Ukrainian side will soon decide how to respond to this provocation, taking into account current practice,” it added.
In recent years, Russia has detained a number of Ukrainian nationals on suspicion of spying but the detention of a diplomat is rare.
Tensions between Moscow and Kyiv have been rising amid a build-up of Russian troops along the border and clashes in eastern Ukraine between the army and pro-Moscow separatists.
Kyiv has been battling Russian-backed separatists in the east of Ukraine since 2014, and clashes have intensified since the start of the year, shredding a ceasefire agreed in last July.
On Friday, Ukrainian President Volodymyr Zelenskyy pressed for peace negotiations.