The war in Ukraine is entering a more destructive phase: a retired army officer

The next phases of the war in Ukraine are likely to be hugely costly for big cities as Russia turns to larger, more indiscriminate weapons and prepares for brutal urban battles.

Despite fierce Ukrainian resistance, cities are surrounded and Russian forces are already using weapons such as artillery to bomb them, retired US Army Colonel Jack Jacobs told CNBC’s Squawk Box Asia.

“The Russians will step up their indirect fire on the settlements, especially in Kyiv,” Jacobs said. Indirect fire refers to weapons that are aimed not at a single target but at an area, such as a city. Weapons such as artillery are used in large quantities and destroy large areas.

“And in doing so, they’re going to do something … they didn’t want to do because they wanted to take the city intact,” Jacobs said. “They will use … the possibility of firing missiles, artillery, missiles and other indirect fire to conquer the Ukrainians in the city. And then try to move.

At this point, the war is moving from one that plays on the Russian military to one that plays on the strengths of the Ukrainians. But it will also be a much more destructive war, because it will be fought up close in urban areas.

Russia’s military culture focuses training on open field operations, Jacobs said, while Ukrainians – including many of its civilians – have long been preparing for a door-to-door battle in the cities themselves.

“Ukrainians knew from the beginning that this could ultimately be reduced to their ability to destroy Russian forces in built-up areas,” said Jacobs, who survived the city battles as an officer in the Vietnam War.

Unfortunately, this scenario will cost a terrible price for the cities of Ukraine, which are still full of civilians, although many have fled.

John Spencer, an expert on urban warfare at the Institute of Contemporary Warfare at the U.S. Military Academy, told NBC News that once Russian troops are in the cities in large numbers, “it will be really ugly.”

“The Russians will not be able to take Kyiv just by bombing it,” Spencer told NBC. “They’ll have to get soldiers there.”

Russian President Vladimir Putin has already shown a personal willingness to destroy a city – even within Russia’s borders – if necessary to achieve its political goals.

As Russia’s prime minister in 1999, Putin launched a brutal military campaign against Chechnya to keep the province under Moscow’s control. Russian troops largely destroyed its capital, Grozny. Thousands of civilians were killed there.

“I think it will be difficult for Putin to bring this back,” Jacobs said. “He will continue until he does … at a huge cost. For Ukraine, for Russia and maybe even for allies.”

Other major cities in Ukraine are probably already surrounded by Russian forces, according to a Update from the UK Department of Defense released on Tuesday.

“Ukrainian forces continue to hold the cities of Kharkiv, Kherson and Mariupol, but now all three cities are probably surrounded by Russian forces,” the ministry said.

The Ukrainian government said on Tuesday that Kharkiv, the second largest city, was the target of heavy shelling by Russian forces, NBC News reported. This city is home to about 1.5 million people.

At least 10 people were killed and 35 wounded on Tuesday by Russian missiles in central Kharkov, Interior Ministry adviser Anton Herashchenko said in a social media post.

Kyiv is not yet surrounded, but a huge, 40-kilometer Russian column is moving slowly from north to the city to connect with forces to the south and encircle the capital.

Ukrainian troops put up fierce resistance against the Russian invaders north of Kyiv, but without sufficient air power, they failed to force the convoy to retreat.

The ongoing battle over the convoy is critical for Ukrainians and Kyiv. It is important, Jacobs said, that more Western weapons reach Ukrainians before they are cut off.

“If the Ukrainians manage … to bring enough weapons to carry this convoy, they tend to stop it long enough for the Ukrainians to be supplied by the West,” he said.