KYIV, Dec 22 - Ukrainian military forces have conducted combat drills with U.S.-made Javelin anti-tank missiles in a conflict area with separatists in eastern Ukraine as tensions run high with Russia, Ukrainian Dom television channel said on Wednesday, Reuters reported.

Javelin missiles are believed to be the most effective weapon against Russian tanks as the drills come amid speculations that Russia may be preparing an attack to invade Ukraine.

Ukraine, which seeks to join the North Atlantic Treaty Organization (NATO), has since 2018 received a series of consignments of U.S. ammunition and Javelin missiles, prompting criticism from Moscow.

Kyiv accuses Moscow of massing tens of thousands of troops in preparation for a possible offensive, raising fears that a simmering conflict in Ukraine's eastern Donbass region could erupt into open war 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 practiced complex flight tasks, it said, which included mid-air refueling at altitudes ranging from 2,000 to 6,000 meters 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. (rt/ez)