Russia has relied far more heavily on less sophisticated, so-called “dumb” bombs than it has on its arsenal of precision-guided munitions in its punishing war on Ukraine, CNN reported.

It’s a dynamic that US officials are watching closely for clues about the state of Russia’s military — as these indiscriminate weapons kill scores of civilians.

Russia has used a combination of missiles, artillery and rocket launchers to pummel major Ukrainian cities over the past two weeks, Lt Gen Scott Berrier, the head of the Defense Intelligence Agency, told the Senate Intelligence Committee on Thursday.

On Friday, Russia launched a barrage of missile attacks on a wide range of targets across central and western Ukraine, causing substantial damage and using what Russia’s defence ministry said were “high-precision long-range weapons”.

But the number of “precision-guided munitions that are being dropped from aircraft… is small,” Berrier said, CNN reported.

The US and Western officials said they don’t know why Russia hasn’t used more of these sophisticated weapons, which its Su-34 fighter-bomber fleet regularly employed, along with other unguided bombs in Syria.

It’s an approach some US military and intelligence officials say could signal another surprising weakness in Russia’s military campaign — or simply a terrifying willingness to employ brutal tactics that lead to countless civilian deaths in a war that many officials think could last weeks or even months.

“It’s hard to say at this point whether that’s driven by expense, if that’s driven by a lack of inventory or if that’s just driven by a desire to be more brutal in the use of force,” a senior NATO official said on Thursday, calling it a “big question”, CNN reported.

Precision-guided munitions, or PGMs, are more expensive, time-consuming and complex to produce than unguided munitions and there has long been speculation that Russia’s stockpile is relatively limited. It is possible, some outside analysts say, that Russia is simply holding its PGMs in reserve for later in the conflict – or as an emergency precaution in case Russia finds itself in conflict with NATO.