KYIV — Ukraine"s army is trying to repel a full-scale Russian invasion, with fierce battles taking place close to the capital Kyiv. Blasts are being reported in Kyiv early Friday, with a Ukrainian official saying the country"s capital has been hit by cruise or ballistic missiles. Fighting is raging at an airfield on the outskirts of the city, and it could become a springboard for the Russian army into Kyiv if its troops seize it. Russia"s full-blown military invasion of Ukraine brought an international outcry on Thursday with NATO condemning a "brutal act of war" and G7 leaders calling it a "serious threat to international order". Brussels and Washington have moved to impose further sanctions on Moscow, targeting finance and business. A day of fighting has seen clashes and casualties reported around the country including near the capital Kyiv. Ukraine has said Russia has taken control of the Chernobyl nuclear plant. Civilians have been seen trying to flee major cities. The Russian assault is being fought on several fronts after it attacked from the east, north and south on Thursday. Russian mechanized forces that had entered Ukraine through Belarus were about 20 miles (32 kilometers) from Kyiv, top Biden administration officials told House lawmakers in a briefing Thursday. The officials described another Russian element that entered Ukraine from Russia being a bit further away, but that both were headed toward Kyiv with the goal of encircling the city and potentially toppling the Ukrainian government, according to a lawmaker on the call. A long convoy of vehicles has been moved across a military pontoon bridge over the Pripyat River near the Ukrainian-Belarussian border, according to new satellite images from Capella Space. The images, taken at 9:57 p.m. Kyiv time on Thursday, show the vehicles lined up on the southern shore of the Pripyat River. Ukraine says dozens of people have been killed, while thousands have fled. Ukrainian President Zelensky said 137 Ukrainian citizens — both soldiers and civilians — died on Thursday. City residents are spending the night in underground shelters amid air-raid warnings. Moscow launched the offensive in the early hours of Thursday morning, shortly after President Vladimir Putin declared war in a dramatic televised address. He threatened any country attempting to interfere with "consequences you have never seen". Air and missile strikes rained down on cities and military bases, before tanks rolled in across three sides of Ukraine"s vast border. It followed weeks of escalating tensions, as Russia massed troops around the country. President Zelensky, meanwhile, vowed to continue fighting. He said "a new iron curtain" was falling into place and his job was to make sure his country remained on its western side. Zelensky ordered conscripts and reservists in all of Ukraine"s regions to be called up to fight. The country"s defence minister urged anyone who was able to hold a weapon to join the effort to repel Russia. Western intelligence officials earlier warned that Russia was building an "overwhelming force" to take control of the city. Ukrainian presidential adviser Mykhaylo Podolyak said the Chernobyl nuclear site itself had been lost following a "fierce battle". The UK"s Ministry of Defense said Ukrainian forces were putting up "a staunch resistance" to the invasion but that "heavy casualties" had been suffered by both sides. The toll on civilians quickly became apparent on Thursday, as thousands moved into neighbouring countries such as Moldova, Romania, Poland and Hungary to escape the conflict. UN estimates suggest that more than 100,000 people have already fled from their homes. "We don"t understand what we should do now," one woman called Svetlana told the BBC. "We"re now going to a place where we can be safe and we hope we can leave safely." Human rights groups warned prior to the invasion that an attack could trigger a major refugee crisis in Europe. In Kyiv, which is home to almost three million people, warning sirens have been blaring out as traffic queues to leave the city. Hundreds of people are seeking shelter for the night in metro stations, bomb shelters and basements. French President Emmanuel Macron held a telephone call with his Russian counterpart, in what was Putin"s first conversation with a Western leader in days. Macron demanded an "immediate halt" to the offensive and threatened Mr Putin with "massive sanctions", the French government said. The Kremlin, however, simply said the pair had a "serious and frank exchange of views". — BBC