Russia has detained a Ukrainian diplomat for allegedly receiving classified information from a database of the country's main security agency.

The move comes amid heightened tensions between the two foes amid a Russian troop build-up close to the Ukrainian border.

The Federal Security Service, or FSB, said in a statement Saturday that Alexander Sosonyuk, Ukraine's consul in St. Petersburg, was taken into custody a day earlier.

The intelligence agency added that Sosonyuk was caught "red-handed" during a meeting with a Russian in which he received "information of a classified nature contained in the databases of law enforcement agencies and the FSB."

"Such activity is not compatible with his diplomatic status and is of clearly hostile nature towards the Russian Federation."

The statement, reported by Russian news agencies, didn't give further details.

Ukraine's foreign ministry said Sosonyuk was held for several hours, but was now back at the country's consulate in St. Petersburg.

Russia has detained a number of Ukrainian nationals on suspicion of spying in recent years but the detention of a diplomat is rare.

Neighbors move closer to the edge

The detention comes amid escalating tensions between Russia and Ukraine amid a Russian military buildup along the border with the eastern Ukraine region, which is under the control of Russia-backed
rebels.

Kiev has been battling the separatists since 2014, and clashes have intensified since the start of the year, shredding a ceasefire that was agreed last July.

Concern has been mounting that the long-simmering conflict could spiral back into wider fighting, and Ukrainian President Volodymyr Zelenskyy has asked the West for help.

mm/ (AP, AFP)