“I’m afraid that there are very few examples in recent history—Baghdad in 2003 being one of them—where an invader has taken a major city by force against a determined defense without using heavy fires and doing extensive damage,” said Justin Bronk, the research fellow for air power and technology at the U.K.’s Royal United Services Institute. He told The Daily Beast that the Russians have not yet used the overwhelming superiority of their air force. In a report for RUSI, he wrote: “The fact that there have only been a few confirmed sightings of Russian fixed wing sorties over Ukraine should not obscure the fact that the VKS fixed wing fleets remain a potentially highly destructive force and one that could be unleashed… at short notice over the coming days.”

There have also been reports of the Russians moving thermobaric missile-launchers, which fire rocket explosives that set the air around them on fire. These weapons, considered illegal under the Geneva Conventions, are many times more powerful than traditional explosive weapons that have been seen in Ukraine so far. If they are used, it would suggest that the Kremlin is willing to raze the historic cities of Kharkiv and Kyiv to the ground and inflict extraordinary numbers of civilian casualties in the process.