MOSCOW (AFP, REUTERS) - Russian Foreign Minister Sergei Lavrov on Wednesday (March 23) said sending peacekeepers to Ukraine could lead to a direct confrontation between Russia and the Nato military alliance.

Poland said last week that it would formally submit a proposal for a peacekeeping mission in Ukraine at the next Nato summit.

“I hope they understand what they are talking about,” Mr Lavrov told staff and students at the Moscow State Institute of International Relations.

“This will be the direct clash between the Russian and Nato armed forces that everyone has not only tried to avoid but said should not take place in principle.”

Moscow has accused Kyiv of stalling peace talks by making proposals unacceptable for Russia. Ukraine has said it is willing to negotiate but will not surrender or accept Russian ultimatums.

Mr Lavrov said Ukrainian authorities were backing away from their own proposals at the talks, making it difficult to achieve a breakthrough.

“The talks have started, they are difficult because the Ukrainian side... constantly changes its mind and backs away from its own proposals,” Mr Lavrov said.

"It’s hard to avoid the impression that our American colleagues are holding their hand,” Mr Lavrov added, claiming the US “apparently wants to keep us in a state of military action as long as possible”.

Ukrainian President Volodymyr Zelensky said earlier on Wednesday that the talks with Russia were tough and at times confrontational.

He held out hope for negotiations, which have yielded little since the Feb 24 invasion began.  

"It’s very difficult, sometimes confrontational," he said. "But step by step we are moving forward." 

Separately, the head of the International Committee of the Red Cross is in Moscow for two-day talks with senior Russian officials including Foreign Minister Sergei Lavrov. 

The ICRC's Peter Maurer is expected to raise "pressing humanitarian issues" in Ukraine during the discussions, the agency said. 

Earlier, the Russian Foreign Ministry said Mr Lavrov would meet Mr Maurer on Thursday to discuss the conflict.

“Mr Maurer plans to speak about the pressing humanitarian issues to be addressed to alleviate suffering of people affected by the conflict in Ukraine,” the ICRC said.

The agency was seeking to increase respect for international humanitarian law and within its mandate as a neutral intermediary to “address humanitarian issues and facilitate dialogue between all sides".

Meanwhile, the West plans to announce more sanctions against the Kremlin amid a worsening humanitarian crisis.

Intense Russian air strikes are turning besieged Mariupol into the "ashes of a dead land", the city council said on Tuesday, as street fighting and bombardments raged in the port city.

Hundreds of thousands are believed to be trapped inside buildings, with no access to food, water, power or heat. Both civilians and Ukrainian troops were coming under Russian fire, said regional governor Pavlo Kyrylenko. 

Russian forces and Russian-backed separatist units had taken about half of the port city, normally home to around 400,000 people, Russia's RIA news agency said, citing a separatist leader.

Russian President Vladimir Putin’s incursion into Ukraine has forced more than 3.5 million to flee, brought the unprecedented isolation of Russia’s economy, and raised fears of wider conflict in the West unthought-of for decades.

Mariupol has become the focus of the war that erupted when Mr Putin sent his troops over the border on what he calls a "special military operation" to demilitarise Ukraine and replace its pro-Western leadership.

It lies on the Sea of Azov and its capture would allow Russia to link areas in the east held by pro-Russian separatists with the Crimean peninsula, annexed by Moscow in 2014.

Mr Putin's 27-day long incursion into Ukraine has forced more than 3.5 million to flee, brought the unprecedented isolation of Russia's economy, and raised fears of wider conflict in the West unthought-of for decades.

Western nations plan to heap more economic pressure on the Kremlin.

US President Joe Biden will join allies in applying additional sanctions and tightening existing ones during his trip to Europe this week, national security adviser Jake Sullivan said on Tuesday.

The United States is preparing sanctions on more than 300 members of Russia’s Lower House of Parliament as soon as Thursday, according to The Wall Street Journal, which cited unnamed officials and internal documents.

"No final decisions have been made about who we will sanction and how many we will sanction," said a White House spokesperson. "We will have additional sanctions measures to announce that will be rolled out in conjunction with our allies on Thursday when the President has the opportunity to speak with them."

Mr Biden’s Europe trip is also set to include an announcement on joint action to enhance energy security on the continent, which is highly reliant on Russian gas, and a visit to Poland to show solidarity with Ukraine’s neighbour. 

One of Mr Putin's closest allies said on Wednesday that the United States aimed to humiliate, divide and ultimately destroy Russia, and vowed the country would never allow that to happen.

Dmitry Medvedev, who served as president from 2008 to 2012 and is now deputy secretary of Russia’s Security Council, said such a plan – if ever achieved – could have catastrophic results for the world.

“Russia will never allow such a development,” he said in a message posted on Telegram.

Having failed to seize the capital Kyiv or any other major city with a swift offensive, Russia is waging a war of attrition that has reduced some urban areas to rubble and prompted Western concern that the conflict could escalate, even to a nuclear war.

Russia's security policy dictates that the country would only use such weapons if its very existence were threatened, Kremlin spokesman Dmitry Peskov told CNN on Tuesday.

"If it is an existential threat for our country, then it (the nuclear arsenal) can be used in accordance with our concept," he said.

Earlier he said "no one" had ever thought the operation in Ukraine would take just a couple of days and the campaign was going to plan, TASS news agency reported.

'Humanitarian catastrophe'

The United Nations human rights office in Geneva said on Tuesday it had recorded 953 civilian deaths and 1,557 injured since the invasion. The Kremlin denies targeting civilians.

Western officials said Russian forces were stalled around Kyiv but making some progress in the south and east. Ukrainian fighters are repelling Russian troops in some places but cannot roll them back, they said.

Russia’s combat power in Ukraine has declined below 90 per cent of its pre-invasion levels, a senior US defence official said on Tuesday, without providing evidence. If confirmed, it would suggest heavy losses of weaponry and growing casualties.

Ukraine says Russian shells, bombs and missiles have struck a theatre, an art school and other public buildings, burying hundreds of women and children sheltering in cellars.

On Wednesday, Ukraine's Deputy Prime Minister Iryna Vereshchuk said agreement has been reached to try to evacuate civilians trapped in several towns and cities through nine "humanitarian corridors". 

Signalling no agreement had been reached with Russia to establish a safe corridor form the heart of Mariupol, she said people wishing to leave the besieged port city would find transport in nearby Berdyansk.

Elsewhere in the country, the governor of the eastern region of Luhansk earlier said agreement had been reached a local ceasefire to evacuate civilians trapped by fighting.

Governor Serhiy Gaidai said on the Telegram messaging app that the ceasefire would come into force on Wednesday at 9am (3pm Singapore time).

Speaking on Ukrainian television on Tuesday, Ms Vereshchuk demanded the opening of a humanitarian corridor for civilians. She said at least 100,000 people wanted to leave Mariupol but could not.

Referring to Russia's earlier demand that the city surrender by dawn on Monday, Ms Vereshchuk said: "Our military are defending Mariupol heroically. We did not accept the ultimatum. They offered capitulation under a white flag."

Kyiv accused Moscow of deporting residents of Mariupol and separatist-held areas of Ukraine to Russia. This includes the "forcible transfer" of 2,389 children to Russia from the Luhansk and Donetsk regions, Prosecutor-General Iryna Venediktova said.

Moscow denies forcing people to leave, saying it is taking in refugees.

In Kherson, a city under Russian control, Ukrainian officials said Moscow's forces were preventing supplies from reaching civilians.

"Kherson's 300k citizens face a humanitarian catastrophe owing to the Russian army's blockade," foreign ministry spokesperson Oleg Nikolenko said on Twitter.

Russia did not immediately comment on the situation in Kherson.

Mr Zelensky meanwhile warned the crisis in Ukraine, one of the world's biggest grain exporters, would bring famine elsewhere.

"How can we sow (crops) under the strikes of Russian artillery?" he told Italian lawmakers.

In an address overnight, he also drew attention to the death of Boris Romanchenko, 96, who survived three Nazi concentration camps during World War II but was killed when his apartment block in besieged Kharkiv was shelled last week.

In killing Mr Romanchenko, "Putin managed to 'accomplish' what even Hitler couldn't," Ukraine's Defence Ministry said.