The US has warned China against assisting Russia's invasion of Ukraine, amid allegations that Moscow has requested military assistance from Beijing.

According to several US officials who spoke on condition of anonymity, Russia requested military weapons from China following its invasion, raising concerns in the White House that Beijing could undercut Western attempts to assist Ukrainian forces in defending their country.

US National Security Adviser Jake Sullivan, who is scheduled to meet with China's top diplomat Yang Jiechi later Monday in Rome, warned Beijing that it would "absolutely" suffer consequences if it assisted Moscow in evading broad sanctions over the Ukraine war.

When asked about Russia's request for military assistance, Liu Pengyu, the spokeswoman for China's embassy in Washington, stated, "I've never heard of that."

Mr Lui stated that China finds the current situation in Ukraine "surprising" and that Beijing "supports and encourages all efforts aimed at resolving the crisis peacefully."

Russia's plea to China raises concerns at a time when diplomatic attempts to settle the Ukraine war have intensified.

Negotiators from Ukraine and Russia are preparing to resume talks after both sides hailed progress, despite Russia's strike on a post near the Polish border and fighting elsewhere.

A volley of Russian missiles struck Ukraine's Yavoriv International Centre for Peacekeeping and Security, a camp located just 25 kilometers from the Polish border and previously used to host NATO military instructors, killing 35 people and injuring 134, a Ukrainian official stated Sunday local time.

Russia's defense ministry reported the destruction of up to 180 "foreign mercenaries" and a huge quantity of foreign weaponry. Reuters was unable to independently verify the reported casualties on either side.

Since February 24, when Russian President Vladimir Putin initiated what he dubbed a "special military operation" to clear Ukraine of dangerous nationalists and Nazis, thousands of people have perished.

The US, which had been monitoring Russia's buildup on Ukraine's borders with increasing anxiety for weeks, claims it was a premeditated, unjustifiable, and illegal "war of choice."

The White House claimed that during a late Sunday telephone discussion, US President Joe Biden and France's Emmanuel Macron reaffirmed their determination to holding Russia accountable for the incursion.

According to the State Department, US Secretary of State Antony Blinken and his Ukrainian colleague, Dmytro Kuleba, also discussed diplomatic attempts to halt Russia's incursion.

Russia and Ukraine both expressed optimism following weekend meetings.

"Russia has begun to engage in constructive dialogue," Ukrainian negotiator Mykhailo Podolyak stated in an online video. "I believe that we will see results in a matter of days."

According to the RIA news agency, a Russian envoy to the discussions, Leonid Slutsky, said they had made good progress and it was feasible the delegations would soon finalize draft accords.

Neither party specified what these might entail. Three rounds of discussions between the two sides in Belarus, the most recent of which took place last Monday, have centered mostly on humanitarian concerns.

Ukrainian President Volodymyr Zelenskiy stated that the two nations' teams had been communicating daily via video link and that a clear objective of his negotiators was to "do everything possible" to arrange for him to see Putin.

"We must persevere. We must struggle. "And we will triumph," Zelenskiy declared in a late-night video address.

While Western nations have sought to isolate Putin through tough economic penalties and arms sales to Ukraine, the US and its allies are anxious about NATO becoming involved in the crisis.

Before daybreak, air raid sirens wailed in a number of Ukrainian towns and areas, including Kyiv, Lviv, Odessa, Ivano-Frankivsk, and Cherkasy.

Authorities in the capital claimed they were stockpiling two weeks' worth of food for the city's 2 million residents who had not yet fled Russian soldiers preparing to encircle it.

According to the regional police chief, an American journalist was shot and killed by Russian forces in the town of Irpin, northwest of Kyiv. Another journalist was wounded.

According to the British defence ministry, Russian naval forces have imposed a remote blockade of Ukraine's Black Sea coast, effectively isolating the country from international marine commerce.

Russian troops were attempting to surround Ukrainian forces in eastern Ukraine as they advanced from the port of Mariupol in the south to the second city of Kharkiv in the north, the statement continued.

Over 2.5 million people have fled over Ukraine's borders, and hundreds of thousands are stuck in besieged cities as a result of Russia's incursion.

"It's terrifying how violent and inhuman it is," Olga, a Kyiv refugee who crossed into Romania, told Reuters.

According to the United Nations, at least 596 civilians have died since the invasion began, and the death toll is likely much higher due to the difficulty of confirming deaths in areas such as Mariupol.