Russia is gaining ground in Kharkiv with daily “glider bomb” attacks and there is little Ukraine can do about it.

Launched from the sanctuary of its own airspace, Russia used 1.5-ton “glider bombs” to gain ground and wreak havoc in Ukraine's second-largest city.

And there's not much Ukraine can do right now to stop them.

Russia's large, cheap, modernized Soviet-era bombs have become one of its most effective weapons during a full-scale invasion.

They contributed to the fall of the strategic town of Avdiivka in February and are now used daily in devastating assaults in Kharkiv.

Local police in the area called them “superweapons,” saying they destroyed entire streets in one fell swoop.

Two were used in an attack on a crowded DIY hardware store in the city of Kharkiv this weekend, leaving at least 14 dead and dozens injured, according to Ukrainian authorities.

President Volodymyr Zelenskyy says they are now Russia's main tool of war.

Moscow's new attacks in northeastern Ukraine come as kyiv is still reeling from stalled Western aid.

And Mr. Zelensky warned that the situation was about to get worse.

On Sunday, he said Moscow's forces were focusing on a new ground offensive in the region, calling on the West to step up its support.

But even with the right weapons, Ukraine faces U.S. restrictions to defend against cross-border attacks.

Analysts say the war has reached an inflection point and Ukraine's victory or defeat could be decided in the coming months.

What are hover bombs?

Glide bombs usually start out as old-fashioned “dumb bombs”, fitted with wing kits and satellite navigation guidance systems to give them “smart” accuracy.

Russia has dipped into its old Soviet stockpiles to breathe new life into its FAB-500 and FAB-1500 heavy iron bombs.

Rather than being dropped overhead, their outstretched wings allow them to glide 50 to 70 kilometers through the air at high speed to reach a target.

And they come with explosives weighing up to 500 kilograms, which leave craters about 20 meters wide and 6 meters deep.

Malcolm Davis, senior defense analyst at the Australian Strategic Policy Institute, says Russia uses these weapons for two main purposes.

“Terrorizing the civilian population by hitting civilian targets – hospitals, schools, that sort of thing,” he told the ABC.

Although their range pales in comparison to cruise missiles, glide bombs are significantly cheaper.

They could be equipped for as little as $20,000 ($30,000).

Mr Zelensky said more than 3,200 guided bombs were used against Ukrainian targets in April alone, calling them Russia's “main instrument” in its attacks.

Authorities in Kharkiv told Al Jazeera over the weekend that bombs were being thrown toward the city every 10 to 20 minutes.

Why can't Ukraine stop them?

Glide bombs are not particularly sophisticated, nor are they new.

Marcus Hellyer, senior analyst at the Australian Strategic Policy Institute (ASPI), says it is a standard weapon that even Australia has in its stockpiles.

Ukraine has more accurate versions of its Western allies, including the US Joint Direct Attack Munition (JDAM) and new long-range GLSDB bombs.

But GLSDB glide bombs launched from the ground would be destroyed by Russian electronic jamming.

What makes Russian glide bombs particularly effective is their positioning and policy.

The city of Kharkiv is 40 km from the border, so glide bombs can be used without Russian planes leaving their airspace.

“The Russians have a lot of aircraft, which allows them to stay outside the Ukrainian air defense network and just bring bombs in,” Dr. Hellyer said.

Not only are they launched beyond the range of most Ukrainian air defense systems, but there is another major problem: the United States has imposed constraints on Ukraine for using its weapons in Russia.

The Institute for the Study of War (ISW) warned that US policy restricting the use of weapons in Russia “severely undermines Ukraine's ability to defend itself.”

Since May 10, Russian forces have captured several villages near the border and entered the town of Vovchansk.

And Moscow continues to step up its strikes across the region, including in the city of Kharkiv, home to about 1.4 million people.

“It is not possible to defend Ukrainian territory without defeating the threat of hover bombs,” George Barros, head of the ISW's Russia and Ukraine portfolio, reported last week.

Is Ukraine losing?

When US Secretary of State Antony Blinken visited Ukraine earlier this month, he admitted that the country was facing a “particularly difficult time.”