President Vladimir Putin has ridiculed the Ukrainian army as NATO’s “foreign legion”, ignoring Western pressure to rein in a pro-Russian insurgency that has gone on the offensive across eastern Ukraine.

Putin’s comments came as an emergency meeting of the Western alliance’s NATO-Ukraine Commission was called to discuss a surge in fighting that has led to a spate of civilian casualties and rapidly growing pressure on Ukraine’s troubled military.

Another 12 people were reported killed Monday, including seven Ukrainian soldiers, as Kiev accused the pro-Russian rebels of firing more than 100 times over the past day on both military positions and civilian areas.

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Fighting was said to be particularly intense near the government-held city of Debaltseve, halfway between the rebel strongholds of Donetsk and Lugansk, where the military said separatists were attacking with tanks and multiple rocket launchers.

Western governments and Kiev accuse Moscow of arming, training and fighting alongside the rebels. Russia denies any direct involvement, although repeated sightings of large numbers of sophisticated heavy weapons being used against Ukrainian forces has stretched the credibility of those denials.

Putin, on a visit to Saint Petersburg, claimed Ukrainian men wanted to flee to Russia because they did not want to become “cannon fodder” in an army that he described as mostly “volunteer nationalist battalions”.

“In essence, this is not an army, this is a foreign legion – in this particular case NATO’s foreign legion, which of course does not pursue the objective of serving Ukraine’s national interests,” Putin said.

He said the aim was “Russia’s containment” and that the Ukrainian government was not interested in a peaceful settlement.

NATO head Jens Stoltenberg later dismissed the comments as “nonsense”.

“The foreign forces in Ukraine are Russian,” Stoltenberg told a press conference at the alliance’s headquarters in Brussels. “So I think that is in a way the problem, that there are Russian forces in Ukraine and that Russia backs the separatists with equipment.”

The unravelling of a September truce deal has picked up pace in the last few days, with the main rebel leader in the Donetsk region last week announcing he would no longer take part in peace talks and planned to seize more territory.

On Saturday, a barrage of rocket fire killed 30 people in a residential area of Mariupol, the last major city in the country’s two separatist provinces still controlled by Kiev.

Analysts say that if rebel forces did capture the city, they would then be close to creating a land corridor linking Russia to the Black Sea peninsula of Crimea, another Ukrainian province that Moscow annexed last March.