The Russian Foreign Ministry says a Molotov cocktail has been thrown at the Russian Consulate in Ukraine’s Lviv, calling the attack “an act of terrorism.”

The ministry said on December 24 that it summoned Ukraine’s charge d’affairs to protest over the attack and demanded apologies from Kyiv.

Ukrainian police said they had launched a probe into the matter, which they described as "hooliganism.”

The incident comes as tensions have escalated between Kyiv and Moscow after Russia massed about 100,000 combat-ready troops near its border with Ukraine in what the United States has called a possible prelude to an invasion.

New satellite images captured by a private U.S. company revealed that Russia has in recent weeks continued stationing more tanks, mobile rocket artillery systems, and advanced short-range ballistic missile batteries near the border as well as on the Crimean Peninsula, which Russia illegally annexed from Ukraine in 2014.

The images released by U.S.-based Maxar Technologies on December 23, showed a base in Crimea packed with hundreds of armored vehicles and tanks as of December 13. A Maxar satellite image of the same base in October showed the base was half empty.

Asked about the military build-up, Kremlin spokesperson Dmitry Peskov said on December 24 that Moscow was acting to defend its own security.

Based on reporting by Reuters and TASS