More than 2.31 million people have been forced to flee Ukraine since Russian forces invaded on Feb. 24, according to the latest figures from the United Nations refugee agency.

The tally from the U.N. High Commissioner for Refugees (UNHCR) amounts to just over 5% of Ukraine's population -- which the World Bank counted at 44 million at the end of 2020 -- on the move across borders in 15 days.

More than half of the refugees are in neighboring Poland, UNHCR figures show.

-ABC News' Zoe Magee

The United Kingdom has added Russian oligarch Roman Abramovich, owner of the Chelsea Football Club, to its list of sanctioned individuals as part of its response to Russia's invasion of Ukraine.

Abramovich was one of seven prominent Russians to be hit with fresh sanctions on Thursday, including travel bans and asset freezes. Igor Sechin, head of Russian state-owned oil firm Rosneft, Alexei Miller, head of Russian state-owned natural gas giant Gazprom, and Oleg Deripaska, who owns part of Russian mining company En+ Group, were also targeted. The measures are worth an estimated 15 billion pounds ($20 billion), according to a press release from the U.K. Foreign, Commonwealth and Development Office.

U.K. Prime Minister Boris Johnson said "there can be no safe havens" for those who support Russian President Vladimir Putin's war in neighboring Ukraine.

"Today's sanctions are the latest step in the U.K.'s unwavering support for the Ukrainian people," Johnson said in a statement Thursday. "We will be ruthless in pursuing those who enable the killing of civilians, destruction of hospitals and illegal occupation of sovereign allies."

The move effectively derails Abramovich's plan to sell his London-based professional soccer team, which he had announced earlier this month. Under the sanctions, Chelsea won't be able to sell new tickets for matches, including games in the upcoming UEFA Champions League, and the club's merchandise stores will be closed. Player transfers and new contracts are also banned.

According to the updated list of sanctions targets published by the U.K. Treasury's Office of Financial Sanctions Implementation, Abramovich is allegedly "associated with a person who is or has been involved in destabilizing Ukraine and undermining and threatening the territorial integrity, sovereignty and independence of Ukraine," namely Putin, with whom Abramovich allegedly "has had a close relationship for decades." Abramovich has denied having strong ties to the Russian leader.

"This association has included obtaining a financial benefit or other material benefit from Putin and the Government of Russia," the document alleges. "This includes tax breaks received by companies linked to Abramovich, buying and selling shares from and to the state at favourable rates, and the contracts received in the run up to the FIFA 2018 World Cup."

-ABC News' Guy Davies and Victor Ordonez

The top diplomats from Russia and Ukraine failed to reach a deal for a cease-fire during talks in Turkey on Thursday.

Russian Foreign Minister Sergey Lavrov and Ukrainian Foreign Minister Dmytro Kuleba held separate press conferences after their meeting in the southern Turkish city of Antalya. Kuleba told reporters they were unable to agree on a cease-fire and that Russia was still demanding Ukraine change its constitution to formally give up its ambitions to join the European Union or NATO. He described the meeting with his Russian counterpart as "difficult."

"We can't end the war if the country that carried out the aggression is not willing to do so," Kuleba said. "Today, I heard that the issue of a cease-fire is linked to Putin's demands. Ukraine has not surrendered and will not surrender."

"We are ready for diplomacy," he added. "But while there isn't one, we will firmly defend ourselves, protecting our people from Russia aggression. I hope that today's format will continue if Russia is ready for a constructive dialogue."

Lavrov, however, told reporters that "nobody actually planned to negotiate a cease-fire" during the meeting.

"If the goal of the meeting was to ask these questions, let's stop firing and let's arrange humanitarian corridors -- not the way Russia has proposed, but the way the Ukrainian side wants this," Lavrov said. "And if all of this is being done just to tell journalists later that all their good intentions failed, then perhaps this fits the logic of Ukrainian policy and diplomacy of which I've spoken: outward effects are designed for the public's momentary perception and substitute real work."

Meanwhile, Lavrov continued to blame Ukraine and the West for the crisis. He claimed that Russian forces "did not attack Ukraine" and "do not plan to attack other countries."

"But we just explained to Ukraine repeatedly that a situation had arisen that posed direct security threats to Russia," he told reporters. "Despite our years-long reminding, persuasion, calls, no one listened to us."

He said the agreement on the daily opening of humanitarian corridors in Ukraine "still stands," but that the evacuation routes and timings are determined by the Russian commanders on the ground. He also made clear that Russia considers the peace talks with Ukraine taking place in neighboring Belarus are the main format for any negotiations. While Moscow hasn't ruled out direct talks between Russian President Vladimir Putin and his Ukrainian counterpart, Volodymyr Zelenskyy, Lavrov said there must first be substantial progress at the meetings between Russian and Ukrainian delegations in Belarus. A fourth round of those talks in Belarus is planned, but an exact date and time was unclear.

"We stand for any contacts in regard to the problems, which constitute the core of the current Ukrainian crisis, and the search for a way out of it," Lavrov told reporters. "These contacts must have an added value, we believe they will never be used ... to replace or depreciate the real, principal negotiating track, which is developing in the Belarusian territory at the level of two delegations."

"Today's conversation confirms there is no alternative to this track," he added.

-ABC News' Yulia Drozd and Patrick Reevell

Ukrainian officials said Thursday they are -- once again -- trying to evacuate thousands of civilians through humanitarian corridors under temporary cease-fires, if they will hold.

So far, evacuations in some cities are managing to go ahead while others are already failing, as Ukrainian officials accuse Russian forces of blocking or deliberately firing on the routes.

Ukrainian Deputy Prime Minister Iryna Vereshchuk said seven humanitarian corridors -- from several besieged cities as well as areas north of Ukraine's capital -- have been agreed upon with Russia for Thursday. The question is whether Russian forces will uphold their end of the deal.

An attempt to evacuate the areas north of Kyiv was underway, with buses trying to reach the towns of Irpin, Bucha, Hostomel and Borodyanka. The Kyiv region's administration told ABC News that they were able to evacuate 15,000 people -- primarily from Irpin and the town of Vorzel -- but Russian troops refused to allow access to Bucha, Hostomel or Borodyanka.

Ukrainian officials were also hoping an evacuation would take place Thursday from Mariupol, the hard-hit southeastern port city where the humanitarian situation is arguably the worst, after Russian airstrikes destroyed a children's hospital and maternity ward there on Wednesday. But Petro Andrushenko, an adviser to Mariupol's mayor, told ABC News that no evacuation can happen Thursday because Russian warplanes have launched multiple airstrikes in the city center since the early morning. At least four aircraft had been spotted and around a dozen bombs had fallen, according to Andrushenko.

He said it was "physically impossible" right now to evacuate people "under bombs and bullets." Nevertheless, there were reports that buses have set off in an attempt to reach Mariupol.

Russia has made clear that, despite the alleged humanitarian corridors, it is continuing its operation to "liberate" Mariupol.

Meanwhile, thousands of people are independently leaving Ukraine's second-largest city, Kharkiv, without a humanitarian corridor because the trains are still running and there are ways out of the besieged city.

-ABC News' Patrick Reevell