Russia wants to split Ukraine into two, as happened with North and South Korea, Ukraine's military intelligence chief said on Sunday, vowing "total" guerrilla warfare to prevent a carve-up of the country.
President Volodymyr Zelensky urged the West to give Ukraine tanks, planes and missiles to help fend off the Russian forces, which the Kyiv government said were increasingly targeting fuel and food depots.
Meanwhile ceasefire talks to resume in Turkey on Monday, Ukraine officials said.
U.S. officials continued efforts to soften comments on Saturday from U.S. President Joe Biden, who said in a fiery speech in Poland that Russian leader Vladimir Putin "cannot remain in power".
U.S. Secretary of State Antony Blinken said Washington had no strategy of regime change in Moscow and that Biden had simply meant Putin could not be "empowered to wage war" against Ukraine or anywhere else.
After more than four weeks of conflict, Russia has failed to seize any major Ukrainian city and Moscow signaled on Friday it was scaling back its ambitions to focus on securing the Donbass region of eastern Ukraine, where Russian-backed separatists have been fighting the Ukrainian army for the past eight years.
A local leader in the self-proclaimed Luhansk People's Republic said on Sunday the region could soon hold a referendum on joining Russia, just as happened in Crimea after Russia seized the Ukrainian peninsula in 2014.
Crimeans voted overwhelmingly to break with Ukraine and join Russia -- a vote that much of the world refused to recognize.
"In fact, it is an attempt to create North and South Korea in Ukraine," Kyrylo Budanov, the head of Ukrainian military intelligence, said in a statement, referring to the division of Korea after World War Two.
He predicted Ukraine's army would push back Russian forces.
"In addition, the season of a total Ukrainian guerrilla safari will soon begin. Then there will be one relevant scenario left for the Russians, how to survive," he said.
Ukraine's foreign ministry spokesperson also dismissed talk of any referendum in eastern Ukraine.
"All fake referendums in the temporarily occupied territories are null and void and will have no legal validity," Oleg Nikolenko told Reuters.
Cruel and senseless
Moscow says the goals for what Putin calls a "special military operation" include demilitarizing and "denazifying" its neighbor. Ukraine and its Western allies calls this a pretext for an unprovoked invasion.
The invasion has devastated several Ukrainian cities, caused a major humanitarian crisis and displaced an estimated 10 million people, nearly a quarter of Ukraine's total population.
Tatyana Manyek, who crossed the Danube by ferry into Romania on Sunday with other refugees, said people in her home city of Odesa were "very afraid" but she would have stayed were it not for her daughter.
"It would be very difficult to provide the child with basic living conditions. That's why we decided to leave," she said, clutching a pet dog in her arms.
In his Sunday blessing, Pope Francis called for an end to the "cruel and senseless" conflict.
"We must repudiate war, a place of death where fathers and mothers bury their children, where men kill their brothers without even seeing them, where the powerful decide and the poor die," he said.
Zelensky demanded in a late-night television address on Saturday that Western nations hand over military hardware that was "gathering dust" in stockpiles, saying his nation needed just 1% of NATO's aircraft and 1% of its tanks.
Western nations have so far given Ukraine anti-tank and anti-aircraft missiles as well as small arms and protective equipment, without offering any heavy armor or planes.
"We've already been waiting 31 days. Who is in charge of the Euro-Atlantic community? Is it really still Moscow, because of intimidation?" Zelensky said, suggesting Western leaders were holding back on supplies because they were frightened of Russia.
Ukrainian Interior Ministry adviser Vadym Denysenko said Russia had started destroying Ukrainian fuel and food storage centers, meaning the government would have to disperse stocks of both in the near future.
Appearing to confirm that, Russia said its missiles had wrecked a fuel deposit on Saturday as well as a military repair plant near the western city of Lviv, just 60 km (40 miles) from the Polish border.
The British Ministry of Defense said Russian forces appeared to be concentrating their efforts on encircling Ukrainian troops directly facing separatist regions in the east.
"The battlefield across northern Ukraine remains largely static with local Ukrainian counterattacks hampering Russian attempts to reorganize their forces," the ministry said.
Biden drew criticism for his improvised remarks during a speech in Warsaw that sought to frame the war as part of a historic struggle for democratic freedoms.
"For God's sake, this man cannot remain in power," Biden said of Putin. Earlier he called Putin a "butcher".
U.S. officials tried to walk back the president's words.
"As you know, and as you have heard us say repeatedly, we do not have a strategy of regime change in Russia - or anywhere else, for that matter," Secretary of State Blinken told reporters during a trip to Jerusalem.
The United Nations has confirmed 1,119 civilian deaths and 1,790 injuries across Ukraine but says the real toll is likely to be higher. Ukraine said on Sunday 139 children had been killed and more than 205 wounded so far in the conflict.
Ukraine and Russia agreed two "humanitarian corridors" to evacuate civilians from frontline areas on Sunday, including allowing people to leave by car from the southern city of Mariupol, Ukrainian Deputy Prime Minister Iryna Vereshchuk said.
The encircled port, located between Crimea and eastern areas held by Russian-backed separatists, has been devastated by weeks of heavy bombardment. Thousands of residents are sheltering in basements with scarce water, food, medicine or power.