President Vladimir Putin said that Moscow would be "forced to react" to any such British moves.
The timing of the visit, which coincided with the second day of meetings between China’s leader, Xi Jinping, and President Vladimir Putin of Russia, set the stage for competing displays of support from the East Asian neighbors.
Although many fled in the opening stages of the war, residents have gradually returned to their homes as Russian forces were pushed back from north of the city last year, and the conflict became centered mainly in the eastern and southern parts of Ukraine.
Oleh Zhdanov, a prominent Ukrainian analyst of military affairs, said late on Saturday that he could not detect any immediate signs Kyiv was going to order a retreat from the city.
At 4:00 am (0900 GMT) Sunday -- unbeknown to the world's media, the Washington political establishment or American voters -- the 80-year-old Democrat boarded an Air Force Boeing 757, known as a C-32.
Biden’s trip, where he pledged $500 million in military aid to Ukraine, was a brazen rebuke to Russian President Vladimir Putin who had hoped his military would swiftly overrun Kyiv within days of launching the invasion last year.
US President Joe Biden made a surprise stop at Kyiv to meet Ukraine President Volodymyr Zelensky. This was Biden's first visit to the country since the Russia-Ukraine war started in February 2022. Watch visuals from Kyiv.
Biden promised increased arms deliveries for Ukraine and vowed Washington's "unflagging commitment" in defending Ukraine's territorial integrity.
Following a pattern of heavy aerial bombardment at times of Ukrainian battlefield or diplomatic advances, Russia launched 32 missiles in the early hours, Ukraine's Air Force said.
"(The) IOC is a promoter of war, murder and destruction. The IOC watches with pleasure Russia destroying Ukraine and then offers Russia a platform to promote genocide and encourages their further killings," Podolyak said on Twitter.
Ukrainian military spokesman Yuriy Ignat told local media that several Russian Tu-95 bombers had launched the missile attack from northern region of Murmansk.
Ukraine has a history of graft and shaky governance, and is under international pressure to show it can be a reliable steward of billions of dollars in Western aid.
According to the latest official toll, nine people on board and at least seven on the ground were killed when the French-made Super Puma helicopter went down in Brovary on the eastern outskirts of Kyiv.
Russia, which invaded last February, has been pounding Ukraine's vital energy infrastructure with missiles and drones since October, causing sweeping blackouts and disruptions to central heating and running water as winter bites.
From New Year’s Eve celebrations in New York's Times Square, to Palestinians inspecting the site of a house demolished by the Israeli army in the West Bank village of Kafr Dan, to the body of late Pope Emeritus Benedict XVI lying out in state inside St. Peter’s Basilica at the Vatican, this photo gallery highlights some of the most compelling images from around the world in the past week.
The Ukrainian capital and other cities came under fire from missiles and Iranian-made drones on Saturday, killing four people, and a new attack Sunday killed one in the southern region of Zaporizhzhia.
As a result of overnight strikes on the Ukrainian capital of Kyiv, energy infrastructure facilities were damaged, causing power and heating outages, Mayor Vitali Klitschko said on Monday.
Russia kept pounding Kyiv for the second night in a row, after firing a barrage of missiles over the capital on New Year's Eve night and earlier in the day.
"We are ready to negotiate with everyone involved about acceptable solutions, but that is up to them - we are not the ones refusing to negotiate, they are," Putin told Rossiya 1 state television in an interview broadcast on Sunday.
"At the core of it all is the policy of our geopolitical opponents aiming to tear apart Russia, the historical Russia," Putin said.
“I am in my office,” he said in a video posted to his channel on the Telegram social media app early Friday. “We are working toward victory.”
Many areas of Ukraine have power for only a few hours a day.
Regional governor Oleksiy Kuleba said 80% of the region was without electricity for a second day after Russian drones hit energy infrastructure around on Monday, the latest in a series of attacks on power facilities since October.
"The enemy is attacking the capital," the administration posted on Telegram.
"Please go to the shelters!" Kyiv city's military administration said on Telegram.