As tensions with Russia rise, Ukrainian armed personnel have conducted combat maneuvers with US-made Javelin anti-tank missiles in a battle zone with rebels in eastern Ukraine, according to the Ukrainian Dom television station.

Ukraine, which is seeking membership in the North Atlantic Treaty Organization (NATO), has received a slew of US ammunition and Javelin missiles since 2018, drawing Moscow’s ire.

Kyiv accuses Moscow of amassing tens of thousands of troops in preparation for an attack, stoking worries that a simmering conflict in Ukraine’s eastern Donbass area would erupt into open confrontation between the neighbors.

Russia denies planning any attack but accuses Ukraine and the United States of destabilizing behavior, and has sought security guarantees against NATO’s eastward expansion.

Russia held its own military drills nearby, the Interfax news agency reported on Wednesday. SU-30 fighter jets and SU-24 bombers from the Black Sea Fleet did aerial refueling exercises over Crimea, the Black Sea peninsula which Russia annexed from Ukraine in 2014.

“The flights were conducted in the sky over Crimea,” Interfax quoted Russia’s Black Sea Fleet as saying. Around 20 pilots practised complex flight tasks, it said, which included mid-air refueling at altitudes ranging from 2,000 to 6,000 metres at speeds of around 600 km/h.

Ukrainian top security official Oleksiy Danilov said on Wednesday 122,000 Russian troops were 200 km (124 miles) away from the border with Ukraine.

Danilov told Reuters last week that Russia would need at least 500,000-600,000 soldiers at the border “in order to keep the situation under control in the event of an offensive.”

He also said Russia could increase troop numbers very quickly and at any moment, but would need more than 24 hours to bring enough troops to the border to mount an invasion.

Ukraine is the focus of consultations between Western allies and Russia, which has been urged to open negotiations in the so-called Normandy format, which would bring together representatives of France, Germany, Russia and Ukraine.

Dialogue with Moscow is necessary, be it in the Normandy format or through talks at the Russia-NATO Council, German Foreign Minister Annalena Baerbock said on Wednesday.