Ukrainian President Volodymyr Zelenskyy is on his first visit to Britain since Russia's invasion almost a year ago.
On just his second trip abroad since the start of the war, he met Prime Minister Rishi Sunak and addressed the British parliament.
Earlier he was greeted by Mr Sunak on the steps of his office at Number 10 Downing Street to applause from onlookers, where Mr Zelenskiy thanked Britain for its support "from the first days of the full-scale invasion".
He was also due to meet King Charles III and visit Ukrainian troops training in the country.
The UK is one of the biggest military backers of Ukraine and has sent the country more than 2 billion pounds ($3.5 billion) in weapons and equipment.
The news of his visit comes on a day when Russian forces suffered their deadliest 24 hours of the war so far, according to Kyiv, while Moscow pressed on with an intensifying winter assault in the east, bringing tens of thousands of freshly mobilised soldiers to the battlefield.
The Ukrainian claim of more than 1,000 Russian troops killed over a day could not be independently verified. Russia has also claimed to have killed large numbers of Ukrainian personnel in recent weeks.
The fatality figures came as Ukraine's stock of tanks was bolstered, but not with the promised Leopard 2 tanks sought by Kyiv for months.
German Defence Minister Boris Pistorius visited Kyiv on Tuesday as Berlin, Denmark, and the Netherlands said they would pool funds to restore Leopard 1 tanks from industry stocks and supply them to Kyiv in the coming months.
Mr Pistorius announced the supply of about 80 Leopard 1s this year and about 100 in 2024, more than previously announced.
German Vice-Chancellor Robert Halbeck said separately on a visit to Washington that he expected Ukraine to have a double-digit number of Leopard 1 tanks by March but he was not sure how many of the 178 tanks authorised would be sent in total.
In a joint statement, the defence ministers of Denmark, Germany and the Netherlands said the shipment of the older Leopard 1 tanks was part of an effort "to support Ukraine in their endeavour to withstand Russian aggression".
"[It] will significantly enhance Ukraine's military potential for the restoration of their violated territorial integrity," they said, adding that the delivery would occur "within the coming months" and include logistical support and training.
Tanks and longer-range rockets coming to Ukraine
The Leopard 1, manufactured between the mid-1960s and the mid-1980s, was the first battle tank built for West Germany's Bundeswehr.
The German military has not had any of the tanks since 2003.
The announcement followed Germany agreeing last month to allow countries to re-export the more modern German-made Leopard 2 tanks to Ukraine.
Germany is set to send 14 newer Leopard 2 A6 tanks from its military's current stocks.
The country's Defence Ministry said on Tuesday that the first Leopard 2s could arrive in Ukraine by the end of March.
The first Ukrainian soldiers to be trained on the tanks departed for Germany this week.
Several other European countries have equipped their armies with Leopard 2s. Germany's move following weeks of mounting pressure meant those nations could also give some of their stocks to Ukraine.
Since the New Year, Western countries have pledged hundreds of tanks and armoured vehicles to Ukraine to give it the firepower and mobility to push through Russian lines and recapture territory later this year.
A new US package of weapons is expected to include longer-range rockets, which would give Ukraine the ability to hit Russian supply lines in all of the territory it occupies in Ukraine's mainland and parts of the Crimea Peninsula.
Zelenskyy to visit UK for first time since Russia's invasion
Ukrainian President Volodymyr Zelenskyy will visit Britain on Wednesday, his first trip to the UK since the war began.
The British government says Mr Zelenskyy will meet with Prime Minister Rishi Sunak and address parliament.
The UK is one of the biggest military backers of Ukraine and has sent the country more than 2 billion pounds ($3,5 billion) in weapons and equipment.
Russia warns of 'unpredictable level of escalation'
Ukrainian Foreign Minister Dmytro Kuleba said on Twitter he spoke on Tuesday with US Secretary of State Antony Blinken about new military aid, sanctions on Russia and "the preparations of important events" as the day marking one year since Russia's February 24 invasion neared.
But it will take months before new weapons arrive, and meanwhile Russia has replenished its manpower by calling up reservists.
The Kremlin said Western supplies of arms only widened and extended the conflict.
"The US and its allies are trying to prolong the conflict as much as possible," Russian Defence Minister Sergei Shoigu said on Tuesday in a conference call with military officials.
"To do this, they have started supplying heavy offensive weapons, openly urging Ukraine to seize our territories. In fact, such steps are dragging NATO countries into the conflict and could lead to an unpredictable level of escalation."
His use of the phrase "our territories" appeared to refer to four Ukrainian provinces Russia claimed to have annexed last year, as well as Crimea, which it seized from Ukraine in 2014.
Separately, Russia demanded that the US embassy in Moscow stop spreading what Moscow regards as fake news about the military operation in Ukraine and threatened to expel US diplomats, Russia's state-owned TASS news agency reported on Tuesday.
Both sides claim large death tolls
The Ukrainian military increased its running tally of Russian military dead by 1,030 overnight to 133,190, describing the increase as the highest of the war so far and among 1,900 over two days.
Russia said it had inflicted 6,500 Ukrainian casualties in the month of January.
Although tallies of enemy casualties from either side have typically been seen as unreliable, and Kyiv offered few details of the latest battles, Ukraine's assertion that the day's fighting was the deadliest so far for Russian troops fit descriptions from both sides of escalating close-contact trench warfare.
Close to the town of Marinka, some 30 kilometres from the eastern city of Donetsk, a marine unit of Ukraine's armed forces fired rockets on Russian positions from a Soviet-era launch system.
Soldiers said Russians had changed tactics since arriving in vehicle columns at the start of the invasion.
Kyiv and the West said Russia had been pouring troops and mercenaries into eastern Ukraine in recent weeks in the hope of being able to claim new gains by February 24.
Ukraine expecting Russian strikes on Kharkiv, Zaporizhia
The war is entering its second year at a pivotal juncture, with Moscow trying to regain the initiative while Kyiv holds out for Western tanks to mount a counteroffensive later in 2023.
After failing to capture the Ukrainian capital last year and losing ground in the second half of 2022, Moscow is now making full use of hundreds of thousands of troops it called up in its first mobilisation since World War II.
The last few weeks have seen Russia boast of its first gains in half a year.
But the progress has still been incremental, with Russia yet to capture a single major population centre in its winter campaign despite thousands of dead.
Fighting has focused for months around Ukrainian-held Bakhmut in eastern Donetsk province, a city with a pre-war population of about 75,000.
Russia has made clear progress towards encircling it from both the north and south, but Kyiv says its garrison is holding fast.
Moscow has also launched an assault further south against Vuhledar, a Ukrainian-controlled bastion also in Donetsk province on high ground at the strategic intersection between the eastern and southern front lines.
Ukraine's national security chief, Oleksiy Danilov, said Russia was expected to include the north-eastern Kharkiv or southern Zaporizhia regions as targets of an anticipated offensive.
Reuters/AP/ABC
