The New York Times said on Thursday, citing senior U.S. officials, that classified war documents were posted this week on Twitter and Telegram, which is widely used in Russia.
A Ukrainian official told Reuters the documents contained a "very large amount of fictitious information" and the posts looked like a Russian disinformation operation to sow doubts about the offensive, which requires advanced Western weapons.
"These are just standard elements of operational games by Russian intelligence. And nothing more," presidential official Mykhailo Podolyak said in a statement. The Kremlin did not immediately respond to a request for comment.
The announcement by the presidential office of talks on Friday at the Ukrainian headquarters of the armed forces supreme command attended by President Volodymyr Zelenskiy made no mention of a leak having occurred.
"The participants of the meeting focused on measures to prevent the leakage of information regarding the plans of the defence forces of Ukraine," it said.
It was not clear whether the discussions centred on preventing leaks from within Ukraine or from among the Western partners it now shares information with, after an initial reluctance in the immediate aftermath of Russia's invasion.
The Times said the documents did not reveal when or where the offensive would take place but that the leak could affect trust between the allies as it gave timetables for the delivery of weaponry and Ukrainian troops trained by the West.
They appeared to have been modified in places, overstating American estimates of Ukrainian war dead and underestimating Russian military casualties, the paper said, adding that U.S. officials were working to get the posts taken down.
The White House did not respond to a request for comment. Reuters was not immediately able to review the documents.
Asked to comment, a Pentagon spokesperson said: "We are aware of the reports of social media posts and the department is reviewing the matter."
Three U.S. officials told Reuters in Washington that Russia or pro-Russian elements were likely to have been behind the leak.
One document posted on social media said 16,000 to 17,500 Russian forces had been killed since the invasion. The United States believes the actual figure is much higher, at around 200,000 Russians killed and wounded, officials say.
BAKHMUT AT RISK
British intelligence said earlier that Russian forces were threatening a key supply route to Bakhmut, the focus of their assault for months which Ukraine has said it is defending to wear the invaders down before its counter-offensive.
The Ukrainian military said it was holding on in the city but the situation was difficult.
Zelenskiy said on Wednesday that if his troops came under risk of encirclement they would pull back from Bakhmut - one of the last urban centres in Ukraine's eastern Donetsk province yet to fall to Russian forces.
Donetsk is one of four provinces in eastern and southern Ukraine that Russia declared annexed last year and is seeking to fully occupy in what appears to be a shift in its war aims after failing to overrun the country early in the war.
Friday's daily update from British military intelligence contrasted with the usual emphasis on Ukrainian successes.
"Ukraine's key 0506 supply route to the west of the town is likely severely threatened," it said. Ukrainian military expert Vladyslav Selezniov has said Ukraine will have to pull back if the route for getting supplies in and wounded out is threatened.
Eastern Military Command spokesperson Serhiy Cherevatyi told Reuters Ukraine controlled the situation in Bakhmut and understood Russian intentions.
Western analysts say both sides are losing large numbers of troops in the battle for Bakhmut, a regional transport and logistics hub now largely in ruins.
Zelenskiy told CNN last month that he feared Russian forces would have "an open road" to two bigger cities in Donetsk - Kramatorsk and Sloviansk - if they took Bakhmut.
GIRL'S FATHER DETAINED
Millions of Ukrainians have fled the conflict, which has laid waste to many towns and cities and killed thousands of civilians.
Three civilians were killed and 17 wounded over the past 24 hours in Russian artillery, missile and aerial attacks on 114 settlements in nine regions, the Ukrainian Defence Ministry said.
Authorities in Russian-controlled areas of eastern Ukraine said seven civilians were killed on Thursday in two Ukrainian artillery strikes. Both sides deny targeting civilians.
Moscow says it invaded Ukraine in February 2022 because its moves towards the West threatened Russia's own security, and Russian authorities have since cracked down on internal dissent.
Alexei Moskalyov, a Russian man charged with discrediting the country's army after his daughter drew an anti-war picture, is being held in Belarus, Russian state-owned news agency TASS reported, citing the Russian embassy in the country. Belarus is a close ally of Russia.
The Kremlin says it will not consider peace in Ukraine unless Kyiv accepts the loss of the territories Russia has annexed. Ukraine says it posed no threat to Russia and there can be no negotiations until Russia withdraws all its forces.
Turkey is concerned about the potential intensification of the conflict in the spring, Turkish Foreign Minister Mevlut Cavusoglu told a joint news conference with Russian counterpart Sergei Lavrov in Ankara.
Lavrov reiterated that Russia's security concerns were ignored by the West and said its interests must be taken into account. Asked if he would meet with U.S. Secretary of State Antony Blinken at the United Nations headquarters, Lavrov said Moscow would never refuse serious proposals for dialogue.
(Additional reporting by Tom Balmforth, Don Durfee, Ronald Popeski, Alexander Vasovic, Heather Timmons and Reuters bureaux; writing by Philippa Fletcher; editing by Mark Heinrich and Angus MacSwan)
