By Pavel Polityuk and Aleksandar Vasovic

LVIV/KYIV, Ukraine (Reuters) - The number of Ukrainian refugees was expected to reach 1.5 million on Sunday as Russia continued its attack 11 days after invading Ukraine and Kyiv pressed for further Western action, including more sanctions and weapons.

Moscow and Kyiv traded blame over a failed ceasefire plan that would have let civilians flee Mariupol and Volnovakha, two southern cities besieged by Russian forces. Another round of talks was tentatively planned for Monday as Ukrainians who could escape spilled into neighboring Poland, Romania, Slovakia, and elsewhere.

In a televised address on Saturday night, Ukraine's President Volodymyr Zelenskiy called on people in areas occupied by Russian troops to go on the offensive and fight.

"We must go outside and drive this evil out of our cities," he said, vowing to rebuild his nation. "My confidence in this is reinforced by the energy of our resistance, our protest."

Russian President Vladimir Putin earlier reiterated that he wanted a neutral Ukraine that had been "demilitarised" and "denazified," and likened Western sanctions "to a declaration of war," adding: "Thank God it has not come to that."

Ukraine and Western countries have decried Putin's reasons as a baseless pretext for the invasion he launched on Feb. 24 and have imposed sweeping sanctions aimed at isolating Moscow and crippling its economy.

Ukraine's Foreign Minister Dmytro Kuleba, after meeting with Secretary of State Antony Blinken at the Ukraine-Poland border, said he expected new sanctions and weapons for Ukraine in coming days.

The United States has said it would give Ukraine more weapons and has repeatedly warned it could escalate sanctions, with President Joe Biden seeking $10 billion in emergency funding to respond to the crisis.

Washington is working with Poland as Warsaw considers whether to provide fighter jets to Ukraine, a White House spokesperson said late on Saturday, adding that the United States could replenish Poland's supply of jets if they did, although challenges remain given the contested airspace.

Zelensky had asked for help securing aircraft from European allies in a video call with U.S. lawmakers earlier on Saturday. He also called again for more lethal aid, a ban on Russian oil, a no-fly zone and an end to Visa Inc and MasterCard Inc privileges in Russia, U.S. media reported.

Biden spoke with Zelenski for about 30 minutes on Saturday evening in Washington as Sunday dawned in Ukraine, the White House said. They discussed security, financial support for Ukraine and the continuation of sanctions against Russia, Zelensky wrote on Twitter.

NATO, which Ukraine wants to join, has resisted Zelenskiy's appeals to impose a no-fly zone over his country, saying it would escalate the conflict outside Ukraine.

Seeking to mediate, Israeli Prime Minister Naftali Bennett met with Putin at the Kremlin on Saturday and later spoke to Zelensky, Bennett's spokesperson said.

"We continue dialogue," Zelensky tweeted after the call.

British Prime Minister Boris Johnson issued a six-point plan to respond to Russia's invasion ahead of meetings with leaders from Canada, the Netherlands and Central Europe in London next week.

Turkish President Tayyip Erdogan is expected to talk with Putin on Sunday. Turkey, a NATO member, shares a maritime border with Ukraine and Russia in the Black Sea.

Ukrainian negotiators said a third round of talks with Russia on a ceasefire would go ahead on Monday, although Moscow was less definitive.

Fierce Fighting

Russia's Defense Ministry said its forces were carrying out a wide-ranging offensive in Ukraine and had taken several towns and villages, Russian news agency Interfax said.

Ukraine's military said armed forces "are fighting fiercely to liberate Ukrainian cities from Russian occupiers," counter-attacking in some areas and disrupting communications.

The general staff of Ukraine's armed forces said the military shot down two Russian planes and five helicopters on Saturday and also carried out air strikes against 15 motorized brigades. Reuters had no way to corroborate the claim.

In Kherson, southern Ukraine, the only regional capital to have changed hands since the invasion, several thousand people demonstrated on its main square on Saturday, chanting "Kherson is Ukraine" and demanding Russian forces withdraw.

Eyewitnesses cited by Interfax said Russian troops fired automatic rifles into the air in an unsuccessful attempt to disperse the crowd and later left.

Concerns over nuclear dangers remained after Russia seized Ukraine's Zaporizhzhia nuclear power plant, with a top U.S. official saying on Friday that Russian troops were 20 miles (32 km) from Ukraine's second largest nuclear facility.

Russia was warning the EU and NATO again to stop the "pumping of state-of-the-art weapons systems" into Kyiv, foreign ministry spokesperson Maria Zakharova said, according to RIA.

Putin, in one of several decrees signed on Saturday, also gave his government two days to draw up a list of nations engaged in "unfriendly acts" towards Russia, its news agencies reported.

Visa, Mastercard Exit Russia

The International Monetary Fund warned the conflict would have a "severe impact" on the global economy, driving up energy and grain prices. It said it would weigh Kyiv's request for $1.4 billion in emergency financing as early as next week.

Many Russians, reeling from a 30% fall in the rouble's value, money transfer curbs and the exit of a growing number of Western companies, have expressed fear for their economic future.

Both Visa and Mastercard on Saturday said their credit card operations would be suspended in Russia.

Elon Musk promised to deliver more Starlink satellite internet terminals to Ukraine next week, Zelenskiy said on Saturday, adding he had spoken to the SpaceX chief executive. That could help shore up Ukraine's internet access but also poses potential security risks, experts say.

'Help Us If You Can'

Heavy shelling was heard in the background as residents of Volnovakha tried to flee the fighting.

"Help us if you can, we all want to live, we have kids, husbands, we are mothers and fathers, we are also people," said one local, Larisa. "Where shall I go? What's on me and a bag of things is all I got. That's all I have."

Blinken, following a meeting in Brussels of counterparts from NATO, the G7 and the European Union, met refugees staying in a disused shopping mall in Poland, which has taken in the vast majority of the Ukrainians forced to flee their country.

Ksenia Tymofeeva, 41, worked in a bank in Kyiv until she fled two days ago, leaving behind her husband, also a bank worker, who stayed to fight the Russian invaders.

"He doesn't have any military experience, but it's our homeland," she said at the site near the Poland-Ukraine border.

More refugees crossed into Moldova, Blinken's next stop.

The World Health Organization said 249 civilians had been killed so far and 553 injured as of March 3. It put the number of refugees at 1.2 million and said another 160,000 people had been internally displaced.

"The human cost is likely much higher as access and security challenges make it difficult to verify the actual number of deaths and injuries," it said in a statement.

(Reporting by Pavel Polityuk, Natalia Zinets, Aleksandar Vasovic in Ukraine, Simon Lewis at the Polish-Ukraine border; Olzhas Auyezov in Almaty, Matthias Williams in Medyka, Guy Faulconbridge and William Schomberg in London, John Irish in Paris, Francois Murphy in Vienna, David Ljunggren in Ottawa, Jarret Renshaw, Idrees Ali and Daphne Psaledakis in Washington and other Reuters bureaus; Writing by Susan Heavey; Editing by Daniel Wallis)