Ukraine would struggle to defend itself if a cease-fire froze the front lines with Russia

• Ukraine is exposed to future attacks if the front lines are frozen as part of a cease-fire deal.
• Russia's forces are close to Ukrainian cities, including Kherson and Zaporizhzhia.
• To ensure a lasting cease-fire, Ukraine needs a front it can effectively defend, experts told BI.

A cease-fire in Ukraine is moving closer to reality, but freezing the current front line with Russia would leave it vulnerable to another attack.

As President Donald Trump is set to talk to Russian President Vladimir Putin later Tuesday, military experts warn that simply freezing the front lines as they stand would likely be a prelude to future conflict, not a lasting solution.

This is especially true without security guarantees from the US or enough international peacekeepers to monitor and respond to renewed Russian aggression.

There are few naturally defensible positions between the front line and major strategic targets, meaning the temptation for Russia to break a cease-fire deal and take advantage of Ukraine's fragile defensive situation would be high.

In an assessment on Sunday, the Institute for the Study of War said that "the current frontlines do not provide the strategic depth that Ukraine will need to reliably defend against renewed Russian aggression."

Bryden Spurling, a senior research leader with RAND Europe, told BI that the further west the front line is drawn, the worse for Ukraine given the concentration of strategically and economically vital centers near the front.

"So there is a lot at stake in the position of any frozen lines of conflict for Ukraine's future prospects — not just in defense, but economically," he said.

Russia's grinding offensive

Russia occupies about 20% of Ukraine, mostly in the south and east.

The front line has shifted over the course of the three-year war. In recent months, Russia has been making incremental but steady gains.

The ISW think tank said that Russian forces are close to several major cities. It said they're just across the Dnipro River from Kherson City in south Ukraine, roughly 25 kilometers from Zaporizhzhia City in the east, and 30 kilometers from Kharkiv in the north.

It added that the current front line, which is around 600 miles long, would be expensive to defend during a cease-fire, requiring a bigger Ukrainian military, and more support from Ukraine's allies.

A January report by the New York-based Council on Foreign Relations said that Ukraine could defend itself effectively by creating a "multilayered territorial defense system" that would involve a hardened defense perimeter, rapid-response forces, and enhanced protection for cities and critical infrastructure.

It estimated that this would require about 550,000 active duty Ukrainian military personnel, not to mention another 450,000 in reserve, and would cost between $20-40 billion a year, "comparable to the defense budgets of Israel and South Korea."

However, it did point out that this was considerably less than the current wartime expenditures.

To deter another Russian attack, Ukraine would need to lay extensive defensive lines of mines, trenches, and artillery, and guard them with enough troops to slow down an assault force so it could rush more resources in.

Russia has also hit on a successful mix of weapons including glide bombs and exploding drones to advance against Ukraine, and could use a spell of months to rebuild its stocks.

Spurling said that the shorter and less jagged a front line is, the easier it is to defend, and Ukraine would be seeking to draw the line to take advantage of geographical features that gives its defenders an advantage.

"Done properly, it's a complex undertaking," he said.

On Sunday, the ISW called for the US to back Ukraine in pushing back Russian forces and in establishing a front line along positions that can be more easily defended.

"A ceasefire along more defensible positions would also place Russian forces in a more disadvantaged position for renewed offensive operations, making future Russian aggression less likely," it said.

Peace or fragile truce?

Many specifics of a US-backed cease-fire deal remain unclear, if it indeed gets agreed to by both Russia and Ukraine.

But whatever shape it takes, it's unlikely that any deal that freezes the current front line will hold, Stefan Wolff, a professor of international security at the UK's University of Birmingham, told BI.

He also said that any deal would have to be strong enough to deter Russia from using a cease-fire to rearm and launch a new offensive. If the front line was frozen on its current lines, a strong enough security guarantee from the likes of the US could be a deterrent to Russia, he added.

Measures being discussed by some allies include deploying European troops to back up a peace deal, something Russia opposes.

"If Ukraine is properly armed and gets some sort of security guarantee, even badly fortified lines might become more defensible simply by virtue of the cost Ukraine could impose on Russia in the future," Wolff said.

Spurling added that Ukraine was likely to be more focused on obtaining security guarantees from its allies, rather than the demarcation of the front line.

"If Europe or the US are truly willing to provide a genuine backstop in the case of Russian restarting conflict, then that would pose a major strategic dilemma to any future Russian ambitions in Ukraine," he said, "and dramatically increase Ukraine's capacity to absorb any new invasion."