Russia has upgraded its Iranian-made Shahed-136 drones with 90kg warheads, boosting their destructive capability in the latest sign of deepening co-operation between Moscow and Tehran.

Shahed drones – launched in swarms almost always at night – have become a hallmark of Vladimir Putin’s campaign to cripple Ukrainian infrastructure, triggering blackouts and damaging key power facilities.

The new combined warheads are being built as two different models, but both weighing 90kg. One is being built in Russia, the other in Iran.

The Russian-designed model, known as KOFZBCh, combines cumulative, fragmentation, blast and incendiary effects, meaning it can destroy buildings, scatter deadly shrapnel, spark fires and generate a powerful shockwave.

It is designed not just to destroy a specific target but to cause maximum chaos in its surroundings.

The Iranian version lacks incendiary capability but still delivers a powerful blow, according to Ukraine’s Defence Express.

Pavlo Narozhny, a military expert and founder of Reactive Mail, which provides spare parts to the Ukrainian army, told The Telegraph that Russia needed to make its Shahed drones more powerful to counter protective measures put in place by Ukrainian energy companies.