Belarusian President Alexander Lukashenko arrived on a state visit to China on Tuesday, according to Sputnik, a Russian state-owned news agency.

During his planned three-day visit, Lukashenko will hold a series of meetings with top Chinese officials, according to Sputnik.

Belarus has been an unofficial ally of Russia since the war began.

Lukashenko's visit comes at a time when Western officials have issued warnings about the Chinese government possibly aiding Russia in its invasion.

U.S. Secretary of State Antony Blinken and NATO Secretary General Jens Stoltenberg said they have intelligence showing China is preparing to send lethal aid to Russia.

Last week, the Chinese foreign minister visited Russian President Vladimir Putin in Russia. During remarks at that meeting, Putin said he is planning for Chinese President Xi Jinping to visit Russia this spring.

-ABC News' Natalia Shumskaia

Russian President Vladimir Putin acknowledged Russian military losses from its ongoing invasion of Ukraine during his annual meeting with the federal security service Tuesday.

"Unfortunately, comrade officers, we know that there are losses in our ranks," Putin said.

Putin called on the FSB to provide "support" to the families of soldiers who have died in the war.

"We will always remember their heroism and bravery," he added.

Putin did not say how many soldiers have died in the war and the Russian Ministry of Defense hasn't disclosed an exact number of losses since September 2022 when Defense Minister Sergey Shoigu said just shy of 6,000 troops had died.

Secretary of State Antony Blinken and other State Department officials said Russia has likely suffered 200,000 injured or dead soldiers since the start of the war.

Putin also called on the FSB to make sure its border guard "undertake special efforts to control the Russian state border with Ukraine."

A "special group" is currently deployed at the Russia-Ukraine border, made up of border agencies, the FSB air arm, the Russian Armed Forces and the Russian National Guard, according to Putin.

"Your mission is to prevent any incursions by sabotage groups and stop any attempts to smuggle weapons and ammunition into Russia," Putin told the FSB board.

-ABC News' Tanya Stukalova and Anastasia Bagaeva

Air raid sirens blared for more than five hours in several locations across Ukraine starting late Sunday and lasting until the early morning hours.

Ukrainian air forces shot down 11 out of 14 that Russia launched from the north last night, according to the Air Force of the Armed Forces of Ukraine.

Over the past 24 hours, Russians have launched five missiles and 13 air strikes, according to the General Staff of the Armed Forces of Ukraine.

The Russian troops also launched more than 50 rocket attacks primarily in Kherson and Donetsk regions, which led to "dead and wounded civilians, destroyed civilian houses and damaged civilian infrastructure," according to Ukrainian officials.

Shelling from Russian forces was recorded in more than 25 settlements in the Kharkiv and Luhansk regions, Ukrainian officials said.

-ABC News' Ellie Kaufman

U.S. Treasury Secretary Janet Yellen visited Kyiv Monday and met with Ukrainian President Volodymyr Zelenskyy to reaffirm the U.S.'s financial support to Ukraine.

Yellen announced $1.25 billion in economic and budgetary assistance, which helps the Ukrainian government continue to run, funds payroll for soldiers on the front lines and shores up critical infrastructure, according to the Treasury Department.

Yellen said the money is part of the $45 billion Congress approved for Ukraine in December.

"I bring to Kyiv a clear message from President Biden and the American people: We will stand with Ukraine for as long as it takes," Yellen said in her remarks during her sitdown with Zelenskyy.

Yellen told Zelenskyy that the U.S. will provide over $8 billion in this type of assistance "over the coming months," according to the Treasury Department. A readout of the meeting stated the U.S. will provide $9.9 billion total during the first three quarters of 2023.

-ABC News' Sarah Kolinovsky

U.S. Secretary of State Antony Blinken warned Friday that China is "actively thinking about" providing lethal assistance to Russian forces in war-torn Ukraine.

"We're very concerned that they're thinking about it. Up until now, Chinese companies have provided non-lethal support," Blinken told ABC News' George Stephanopoulos during an interview on "Good Morning America."

"From Day One, President Biden warned President Xi not to provide material lethal assistance to Russia for use against Ukraine or to engage in the systematic evasion of sanctions. And the information we have suggests that they’re now actively thinking about it, which is why we've been public about warning them not to," he added. "It could make a material difference in Russia's capacity on the ground at a time when we want to bring this war to an end, not add fuel to the fire and have it continue."

The U.S. government has "shared a lot of information with other countries, with allies and partners," regarding the fact that China is now considering lethal assistance, according to Blinken.

"We always have to get the balance right between making sure that we're protecting the way we get our information and releasing it," he said. "But we thought it was really important to make clear that China's looking at this. And what they're hearing not just from us but from many other countries around the world is: Don't do it."

The Chinese Ministry of Foreign Affairs released a position paper on Friday, calling for a ceasefire between Russia and Ukraine, the resumption of peace talks, an end to unilateral sanctions and the consideration of sovereignty, territorial integrity and security concerns of all countries. Blinken told ABC News that the U.S. government is "taking a look at it."

"No one wants peace more than the Ukrainians and any proposal that can advance peace is something that's worth looking at," he said. "But, you know, there are 12 points in the Chinese plan. If they were serious about the first one, sovereignty, then this war could end tomorrow."

"China's been trying to have it both ways," he added. "It's on the one hand trying to present itself publicly as neutral and seeking peace, while at the same time it is talking up Russia's false narrative about the war, it is, as I said, providing non-lethal assistance to its companies and now contemplating lethal assistance."