Russian army have taken control of a nuclear plant and the cities of Enerhodar and Berdyansk in the Zaporizhzhia region, the Russian Defense Ministry said on Monday.
The plant's operations continued normally, it said, adding that Russia's air force also gained air supremacy over entire territory of Ukraine.
Ukraine's state-run nuclear company Energoatom on Monday denied reports that Russia has taken over the Zaporizhzhia nuclear power plant, the largest in Europe, Interfax Ukraine news agency said.
"Currently, all four nuclear power plants are under the control of Ukraine and are operating normally. Energoatom is taking all necessary measures to protect the nuclear power plants," Energoatom said.
Last week Russian forces gained control over the site of the former Chernobyl nuclear power plant, site of the world's worst nuclear disaster.
Meanwhile, in Ukraine's capital Kyiv Russia's advance has been slowed by logistical failures and fierce Ukrainian resistance, Britain's Defense Ministry said on Monday.
"The bulk of (President Vladimir) Putin's ground forces remain more than 30 kilometers (19 miles) to the north of Kyiv, their advance having been slowed by Ukrainian forces defending Hostomel airfield, a key Russian objective for day one of the conflict," the ministry said.
"Logistical failures and staunch Ukrainian resistance continue to frustrate the Russian advance."
Heavy fighting continues around Chernihiv, a city in northern Ukraine, and the northeastern city of Kharkiv, the defense ministry said in an intelligence update posted on Twitter. Both cities remain under Ukrainian control, it said.
The Ukrainian military said on Monday that Russian troops had slowed down their offensive as Moscow's assault against Ukraine went into its fifth day.
"The Russian occupiers have reduced the pace of the offensive, but are still trying to develop success in some areas," the general staff of the armed forces said.
Russia invaded Ukraine on Thursday, sending shockwaves around the world. Ukraine forces, backed by Western arms, have managed to slow the advance of the Russian army. The Ukrainian military also accused Russia of launching a missile strike on residential buildings in the cities of Zhytomyr and Chernigiv, cities in the country's northwest and north.
"At the same time, all attempts by the Russian invaders to achieve the goal of the military operation failed," the military said. "The enemy is demoralized and bears heavy losses," the military claimed.
