Some of Ukraine's allies have started wondering whether the counteroffensive against Russia is getting bogged down, to the irritation of Kyiv which says it needs more weapons, not criticism.
Over the past two weeks US media have been quoting anonymous military sources questioning Ukraine's strategy, and saying its armed forces are too dispersed to pierce Russian defensive lines.
"Recently a new narrative has started to take hold in some commentaries on the state of the war, notably from Pentagon officials, to the effect that the offensive is turning out to be a deep disappointment," Lawrence Freedman, professor emeritus at King's College London, wrote last month. "Questions are now being raised about whether this is a war that Ukraine can ever win."
On the record, any criticism remains muted.
"This offensive, as you know, is going slow. It's bloody, it's high casualties on both sides," said Mark Milley, US chairman of the Joints Chief of Staff.
"But the Ukrainians still have a significant amount of combat power in reserve," he told AFP, crediting Ukraine with "at least partial success".
Retired Polish army general Boguslaw Pacek was less circumspect, writing on the Biznesalert website that the current rhythm of the counter-offensive "does not permit the hope that it will meet its targets before the start of the rainy season this year".
Robert Brieger, chairman of the EU Military Committee, went further, telling German daily Die Welt that "the Russians will be able to continue this war for a long time".
He said, "It remains questionable whether Ukraine's full sovereignty can be restored with the means available".
- 'Everyone is an expert' -
The Ukrainian leadership has made it clear it has little patience for the musings of armchair critics, far from the battlefield.
"Everyone is now an expert on how we should fight. A gentle reminder that no one understands this war better than we do," the defence ministry in Kyiv posted on X, formerly Twitter. "We need ammunitions, not advice."
Foreign Minister Dmytro Kuleba said on Thursday that "to criticise the counteroffensive as slow is to spit in the face of the Ukrainian soldiers who give their lives".
Speaking on the margins of an EU ministerial meeting he said: "I suggest that all those who criticise shut up, come to Ukraine and try to liberate a square centimetre of territory themselves".
Experts told AFP they believe the implicit criticism of Ukraine in the US is not gratuitous, but intended to influence public opinion ahead of next year's presidential election there.
"There is a wish for quick results," said military historian Michel Goya. "And to show that American help is making a difference."
Military expert Michael Kofman said that in the US "folks are already positioning themselves for a potential blame game to play out".
In a podcast for the War on the Rocks website, he said that while military strategy was defined by Ukraine, "it is also very much shaped by Western support or lack thereof".
Nobody, experts observed, knows this better the President Volodymyr Zelensky, who has consistently asked for more weapons since the start of the war 18 months ago.
Phrasing is important or risks playing into the hands of Russian President Vladimir Putin, cautioned Phillips O'Brien, a professor of strategic studies at the University of St Andrews in Scotland.
"There is a fundamental difference between saying the counteroffensive is going slowly to saying it's failing," he said. "The failing idea is repeating a definite line of Vladimir Putin, which is aimed at undermining support for Ukraine."
- 'Relationship remains good' -
For now, no high-ranking government or military official among Ukraine's allies has suggested that western support may be faltering.
Even Kuleba's testy comments do not "hint at a fracture", said Ivan Klyszcz, research fellow at the International Centre for Defence and Security in Estonia.
He said, "there have been some questions in Ukraine to the extent to which Kyiv's partners truly share its military objectives" which are the full restoration of its territorial integrity, he told AFP.
But despite those nagging suspicions "so far these questions have not amounted to mistrust, and are generally a background concern," said Klyszcz.
"The relationship remains good," he added.
On Friday, the White House said that Ukraine's forces had made "notable progress" in their southern offensive in recent days.
Criticism of the Ukrainian effort by anonymous officials was "not helpful", said White House national security spokesman John Kirby.