Russia's military said Wednesday that it had seen a surge in people signing up to fight in Ukraine since a deadly terror attack on a Moscow concert hall last month.

The Islamic State (IS) group has claimed responsibility for the attack that killed more than 140 people, the worst such attack in Russia in years.

But President Vladimir Putin has since continued to say, without providing evidence, that Ukraine had a hand in plotting the attack.

"Over the last week and a half, military recruitment points have recorded a significant increase in the number of those wishing to sign contracts with the Russian defence ministry to take part in the special military operation," the defence ministry said Wednesday.

Moscow calls its full-scale offensive on Ukraine a "special military operation".

The ministry said more than 100,000 people had voluntarily signed up to fight so far in 2024 -- including 16,000 in the 10 days after the attack.

"Most candidates indicated that the main motive in signing a contract was a desire to avenge the victims of the tragedy that occurred on March 22," it added in a statement on Telegram.

Kremlin spokesman Dmitry Peskov told reporters the increase in recruitment was "further proof" of Russian society's support for Putin and the offensive.

Kyiv has denied any responsibility for the attack and US officials have told the media that Washington warned Russia of a possible threat to the Moscow suburbs.

But Putin and Russian officials have continued to link the attack with Ukraine and its Western backers.

The assault at the Crocus City Hall venue was the most fatal ever to have been claimed by IS on European soil.

Gunmen stormed the venue, shooting concert-goes before setting the building on fire.

Putin said last year that Russia had more than 600,000 troops fighting in Ukraine. He has also ordered the country to boost its overall troop numbers to 1.32 million from a previous level of 1.15 million.

Defence Minister Sergei Shoigu said last year that he planned to increase the number of contract soldiers -- those who voluntarily sign up, as opposed to conscripts -- to 745,000 this year.

Russian forces have a significant manpower advantage on the battlefield, with Kyiv struggling to match Moscow's intense recruitment drive.

The army offers relatively high salaries and has been accused of targeting recruitment in Russia's poorest regions and in the country's ethnic republics.