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

The United States announced an additional $2 billion military aid package for Ukraine on Friday, as the Eastern European country marks the one-year anniversary of Russia's full-scale invasion.

The new aid package includes more missiles for Ukraine's U.S.-supplied High Mobility Artillery Rocket Systems (HIMARS), additional 155mm artillery ammunition, more Switchblade one-way drones and other military equipment, according to the U.S. Department of Defense.

"One year into a war of aggression waged by a permanent member of the U.N. Security Council, our allies and partners worldwide stand united and resolute," U.S. Secretary of Defense Lloyd Austin said in a statement. "Putin's reckless, illegal war is not just an all-out assault on Ukraine's sovereignty and a historic threat to European security. It is also a direct attack on the system of rules, institutions, and laws that the world built at such great cost after World War II -- a system that rejects aggression and respects the rights of all countries, big and small."

The additional aid is being provided under the Ukraine Security Assistance Initiative (USAI) plan, meaning this equipment and artillery have to be made from scratch before being delivered, which will take time. This is different from the other aid packages that come from existing U.S. military stockpiles and get delivered faster.

With the new aid package, the Biden administration has now provided $31.8 billion in assistance to Ukraine since Russia's war began on Feb. 24, 2022.

"Putin thought that Ukraine’s defenses would collapse, that America's resolve would falter, and that the world would look the other way. He was wrong," Lloyd said. "One year later, Ukraine's brave defenders have not wavered, and neither has our commitment to support them for as long as it takes. Despite the Kremlin's campaign of cruelty, the people of Ukraine have shown stunning bravery, skill, and fortitude. Today and every day, we stand by the courageous Ukrainians fighting to defend their country, and we mourn with those who have lost their loved ones in Moscow's monstrous and unnecessary war."

"Difficult times may lie ahead, but let us remain clear-eyed about what is at stake in Ukraine," he added. "And let us remain united in purpose and in action -- and steadfast in our commitment to ensure that a world of rules and rights is not replaced by one of tyranny and turmoil."

-ABC News' Luis Martinez