Ukraine's biggest mobile network operator, Kyivstar, was hit by what appeared to be the biggest cyber attack of the war with Russia so far, knocking out mobile and internet services for millions.
Kyivstar has 24.3 million mobile subscribers - more than half of Ukraine's population - as well as over 1.1 million home internet subscribers.
Its CEO Oleksandr Komarov said the attack was "a result of" the war with Russia, although he did not say which Russian body he believed to be responsible, and that the company's IT infrastructure had been "partially destroyed".
"War is also happening in cyber-space. Unfortunately, we have been hit as a result of this war," he told a national television broadcast.
Ukraine's SBU intelligence agency told Reuters one of the possibilities it was investigating was that of a cyber-attack conducted by Russian security services.
Russia's foreign ministry did not immediately respond to a request for comment.
Komarov said it was unclear when Kyivstar would be able to restore connection.
"(The attack) significantly damaged (our) infrastructure, limited access, we could not counter it at the virtual level, so we shut down Kyivstar physically to limit the enemy's access," Komarov said.
He added that two databases containing customer data had been damaged and were currently locked.
The company, owned by Amsterdam-listed mobile telecoms operator Veon, said in a statement on Facebook that it was working to repair the outage and was cooperating with law enforcement bodies.
Veon said in a statement it was also investigating the attack and it could not yet quantify the financial impact.
Reuters correspondents in Kyiv suffered disruption to their Kyivstar cellular signal throughout the day on Tuesday.
"The most important thing is that the personal data of users has not been compromised," Kyivstar said in its statement, promising to compensate customers for loss of access to services.
Separately, the co-founder of Monobank, a major Ukrainian payment system, said in a social media post that his company was currently suffering a distributed denial of service (DDoS) attack, but that everything was "under control". He subsequently said that attack had been fought off.
Representatives of PrivatBank and Oschadbank, two major Ukrainian financial institutions, told media outlet Hromadske that part of their ATM machines and card terminals had been affected by the Kyivstar outage.
Ukrainian state bodies and companies have often accused Russia, which is at war with Ukraine, of orchestrating cyberattacks against them in the past.
Zelensky makes plea for US aid to Ukraine
Ukrainian President Volodymyr Zelensky will address the US Congress and the White House to press for more US military aid, but the Republican Party shows little sign of listening to his increasingly desperate pleas.
It comes as Russian forces in southern Ukraine have "advanced considerably" around the village of Novopokrovka in the Zaporizhzhia region, Moscow's occupational authorities said.
Novopokrovka lies some 20km east of Robotyne - which Kyiv said it recaptured in the summer but has since struggled to hold on to.
The Russian offensive has dragged on since the start of the military operation in February 2022, but the front has barely moved in eastern and southern Ukraine this winter.
The Ukrainian push to regain territory lost in the initial Russian invasion has since been slower than expected.
Russia has controlled large swathes of the Zaporizhzhia region since the start of its offensive launched last year.
But the main regional centre of Zaporizhzhia remains under Ukrainian control.
For much of the nearly two years that Ukraine has resisted President Vladimir Putin's onslaught, the United States has led a Western coalition sending billions of dollars in weaponry and ammunition.
US Republicans are ever-more openly rejecting the need to fund Ukraine, saying that President Joe Biden needs to devote more attention to domestic security, particularly in stopping illegal migration over the US-Mexican border.
Republicans are also questioning whether Ukraine should keep fighting at all.
Mr Zelensky, who arrived fresh from a diplomatic push with world leaders at the inauguration of Argentine President Javier Milei over the weekend, will meet Mr Biden at the White House. They will also hold a joint press conference.
Mr Biden is a key supporter of Mr Zelensky, framing the Ukrainian war effort as part of a global struggle between democracies and aggressive autocracies.
However on Capitol Hill, Mr Zelensky will face his real test when he addresses republican and democratic senators, and meets the new Republican speaker of the House, Mike Johnson.
In a speech at the National Defense University in Washington, Mr Zelensky said that politics should not "betray" Ukraine's soldiers and he echoed Mr Biden in saying that the struggle had global implications.
"When the free world hesitates, that's when dictatorships celebrate and their most dangerous ambitions ripen," he said. "They see their dreams come true when they see delays."
"Putin must lose," he said.
Mr Zelensky also met the heads of the International Monetary Fund and World Bank as he seeks to shore up his nation's beleaguered economy.
The IMF announced the release of a new $900 million tranche in an ongoing long-term loan.
Republican senators last week blocked a government request for $106 billion in emergency aid primarily for Ukraine and Israel.
Conservatives said they would refuse the package for these close foreign allies unless democrats and the US government also agreed to far-ranging immigration reforms.
One key republican senator, James Lankford, was quoted by US media saying "we're not going to be able" to get a deal by the end of this week.
However the republican right-wing, led by former president and 2024 presidential candidate Donald Trump, has dramatically soured in a much broader sense against Ukraine's cause.
Influential republicans increasingly question why the United States is supporting what they describe as Ukraine's impossible ambition to drive back all of Russia's invading forces.
"What's in America's best interest is to accept Ukraine is going to have to cede some territory to the Russians and we need to bring the war to a close," said Senator JD Vance, a close Trump ally.
He dismissed as "preposterous" White House warnings that allowing Russia to win in Ukraine would put other eastern European countries, including NATO members, at risk.
There should be no "blank cheque" for Ukraine, Mr Vance said.
"You need to articulate what the ambition is. What is $61bn going to accomplish that $100bn hasn't?"
