 Russia may regain its dominance in Ukrainian sky. Russian 4th generation Su-35 fighter jets are strengthening the dominance of the Russian Federation in the combat zone, which can be a worrying change for Ukraine and its partners. ABC News with references to sources in the Ukrainian government announced it. According to a senior Ukrainian official who spoke, newer generation fighter jets are giving Russia increasing dominance in the skies over the conflict zone in eastern Ukraine. It is a potentially worrying shift for the United States and its allies, since Russia's inability to achieve total air superiority throughout the course of the war has been key to Ukrainian successes on the battlefield. In a briefing with journalists last week, a Western official downplayed the concern, stating that Russia's ability to control the skies has been limited by air defense and surface to air missiles. We're not seeing a huge change in that situation, the official said. The senior official in Kiev said Russia had replaced older models of aircraft with its more modern Su-35. According to the official, the Su-35 is equipped with very effective radar and long-distance rockets, and Russia is using these aircraft to attack Ukrainian jets in the air as well as for ground support operations. Ukraine does not have capabilities to counter this threat, the official added. Russian air superiority is a real risk, the official said, adding that more air defense systems from the United States and its allies is currently priority number one for Ukraine. Two other Ukrainian officials confirmed that Russian dominance of the skies over the combat zone was a top issue, with one official claiming Russia has 12 times more aircraft than Ukraine. This is a problem. What we keep telling the Americans is that in the end there is no other solution than to give us Western fighter jets, one official said.