Russian forces battled for control of a vital energy-producing city in Ukraine’s south on Thursday and also gained ground in their bid to cut off the country from the sea, as Ukrainian leaders called on citizens to wage guerrilla war against the invaders. Video from Enerhodar showed fire and thick smoke rising along the road leading to the city. Residents have been erecting barricades along the road, using cars and tires, to prevent Russian troops from advancing. The mayor of Enerhodar, the site of the largest nuclear plant in Europe, said Ukrainian forces were battling Russian troops on the city’s outskirts. According to Dmytro Orlov, the mayor, self-defense units together with the employees of the nuclear plant and volunteers were on a round-the-clock watch to protect the city. Orlov said Thursday that a big Russian convoy was approaching the city and urged residents not to leave homes. The fighting for …