Russian President Vladimir Putin ordered his defense ministry to put the country's deterrence forces on high alert in light of the rising tensions in Ukraine following the special military operation in Donbass.

"I order the minister of defense and the chief of the general staff to put the deterrence forces of the Russian army into a special mode of combat duty," Putin said at a meeting with the officials responsible for the defense bodies.

Putin, during a meeting with his defense minister Sergei Shoigu and General Staff Chief Valery Gerasimov, accused NATO of stepping up its aggressive rhetoric against Moscow, going beyond what he called the "illegitimate" economic sanctions.

Defense Ministry: Ukrainian military actions violate UN convention

The Ukrainian armed forces are escalating their actions against the Russian Armed Forces, as Kiev began mass using phosphorus-filled ammunition, whose use is prohibited under international law, in a bid to curb the advance of the Russian forces in Kiev near Ukraine's Hostomel airfield, Russian Defense Ministry spokesperson Major General Igor Konashenkov said Sunday.

The Ukrainian armed forces units, "in a desperate attempt to hold back the advance of the Russian troops," have picked up on the mass use of phosphorus ammunition in the Kiev suburbs near the Hostomel airfield, the Russian official told a briefing.

"They use 112 mm shells for D-30 howitzers and rockets for Soviet-made BM-21 Grad systems," Konashenkov added.

This is not the first instance of Ukrainians attempting to kill their own, as Kiev's ships attacked Russian naval vessels transporting surrendered Ukrainian border guards via US UAVs, Moscow's defense ministry spokesperson Major General Igor Konashenkov said Saturday.

Konashenkov also stressed that the use of these munitions is prohibited under the third protocol of the 1980 United Nations Convention on Certain Conventional Weapons.

Ukrainian nationalist units have also killed four soldiers from Kiev's armed forces in Sverodonetsk, Lugansk, to stop them from retreating as Moscow advances throughout Ukraine, he added.

Russia launched a special operation to demilitarize and de-Nazify Ukraine on Thursday, in response to requests from the Donetsk and Lugansk people's republics for assistance in combating Ukrainian troops' aggression.

Russia had for months been warning of the threat posed against it by NATO's attempts to expand eastward, which happened simultaneously with an increase in NATO military activity along Russia's borders, and batches of lethal weapons being sent to Ukraine, prompting Russia to request security guarantees from the West. Washington failed to provide the guarantees.

After the West did not respond to Russia's demands, and amid Ukrainian shelling on the Donetsk and Lugansk People's Republics, President Vladimir Putin initiated a special military operation in Donbass.