KYIV, Ukraine (AP) Russian forces battled for control of a crucial energy-producing city in Ukraines south on Thursday and gained ground in their bid to cut off the country from the sea, as Ukrainian leaders called on citizens to rise up and wage guerrilla war against the invaders.

The fighting at Enerhodar, a city on the Dnieper River that accounts for about one-quarter of the countrys power generation, came as another round of talks between the two sides yielded a tentative agreement to set up safe corridors inside Ukraine to evacuate citizens and deliver humanitarian aid.

The mayor of Enerhodar, the site of the biggest nuclear plant in Europe, said Ukrainian forces were battling Russian troops on the citys outskirts. Video showed flames and clouds of black smoke rising above the city of over 50,000, with people streaming away from the inferno, past wrecked cars, as sirens wailed.

Moscows ground advance on Ukraines capital in the north has apparently stalled, with a huge armored column at a standstill outside Kyiv. And stiffer-than-expected resistance from the outmanned, outgunned Ukrainians has staved off the swift victory that Russia may have expected.

A top Russian officer, Maj. Gen. Andrei Sukhovetsky, commander of an airborne division, was killed in the fighting earlier this week, an officers organization in Russia reported.

But the Russians have brought their superior firepower to bear in the past few days, launching hundreds of missiles and artillery attacks on cities and other sites around the country and making significant gains on the ground in the south as part of an effort to sever Ukraines connection to the Black and Azov seas.