Vladimir Putin told the mothers of Russian soldiers serving in the war that he "shares the pain" of those who lost their sons and told them not to believe "lies" about the invasion of Ukraine.
"I want you to know that I, personally, all the leaders of the country, share this pain. We know that nothing can replace the loss of a son," said Putin.
He added that Mother's Day, celebrated in Russia on Sunday, would be marked this year by "a feeling of anxiety and concern" among the women concerned, whose "thoughts will be with their boys".
The meeting took place in Putin's residence in Novo-Ogarevo, near Moscow, and was the first of its kind since the Russian invasion started on 24 February. The Kremlin rarely refers to losses suffered in Ukraine, and Friday's event came after weeks of criticism posted on social networks by relatives of men mobilised in early autumn.
Olga Tsukanova, the founder of Russia's Council of Mothers and Wives, has accused Putin of excluding the organisation from Friday's meeting.
In a recorded video address, Tsukanova demanded that the president should meet with "real mothers" of those who serve in the country's army as opposed to the women "hand-picked" by authorities for the event.
Many wives and mothers of men drafted into the army have accused the authorities of failing to adequately train or equip their relatives before sending them to the front.
"Life is more complicated than what you see on TV or the internet, where you can't trust anything. There is a lot of false information, deception, lies," Putin told the soldiers' mothers.
"This has always been the case, but taking into account modern technologies, it has become even more noticeable and effective," he added, denouncing "informational attacks".
This echoes laws passed after the start of the offensive in Ukraine that punish with heavy prison sentences those accused of spreading "false information" about the army or "discrediting" it.
President Putin also revealed that he sometimes chats by phone to soldiers taking part in the fighting in Ukraine.
He said he was "surprised" by "their mood" and "their attitude to the matter."
"They give me good reason to say that they are heroes, it's true," Putin added.
Russian Defence Ministry said earlier that a total of 300,000 men have been drafted in the partial call-up announced by Putin on 21 September, and that so far 87,000 of them have been deployed to Ukraine.
Activists and reports by Russian media said many of the draftees were inexperienced, were told to procure basic items such as medical kits and flak jackets themselves, and did not receive training before they were sent off to fight.
Some were killed within days of being called up.