Ukraine's President Volodymyr Zelensky visited the newly liberated province of Kherson on Monday, a week after Russian forces withdrew from the region.

Kherson is one of the four Ukrainian territories Russian President Vladimir Putin announced in September would become part of Russia. The U.S. and other Western countries denounced the annexations, saying they violate international law.

The southern Ukrainian region has no electricity or water. The area was the sole regional capital captured by Russia since the invasion began in February.

"The moment is very important," Zelensky told NBC News.

Zelensky said Ukraine was investigating 400 war crimes, allegedly carried out by Russian forces during their eight-month occupation of Kherson.

He added that he hopes for more gains in the months-long war.

"This is the beginning of the end of the war," Zelensky said. "We are step by step coming to all the temporarily occupied territories."

Ukraine Foreign Minister Dmytro Kuleba celebrated the liberation during an address to the European Union Foreign Affairs Council on Monday. Kuleba also called for stronger energy sanctions on Russia, bans on Russian propaganda, and greater defense assistance for Ukraine.

"Sanctions helped us seriously slow down the Russian war machine," Kuleba said. "This proves that the pressure needs to be stepped up."