Russian President Vladimir Putin claimed victory in the battle for Mariupol on Thursday, even as he ordered his troops not to risk more losses by storming the giant steel plant containing the last Ukrainian holdouts in the city.

Instead, he directed his forces to seal off the Azovstal plant "so that not even a fly comes through."

Russian troops have bombarded the southeastern port city since the early days of the war and largely reduced it to ruins. Top officials have repeatedly claimed it was about to fall, but Ukrainian forces have stubbornly held on.

In recent weeks, a few thousand defenders, by Russia's estimate, holed up along with hundreds of civilians in the sprawling steel plant, as Putin's forces pounded the site and repeatedly issued ultimatums ordering their surrender.

But on Thursday, as he has done before, the Russian leader seemed to shift the narrative and declared victory without taking the plant, which covers 11 square kilometers (4 square miles) and is threaded with some 24 kilometers (15 miles) of tunnels and bunkers.

"The completion of combat work to liberate Mariupol is a success," he said in an appearance with his defense minister. "Congratulations."

Ukraine scoffed at the idea of a Russian victory.

"This situation means the following: They cannot physically capture Azovstal. They have understood this. They suffered huge losses there," said Oleksiy Arestovich, an adviser to Ukrainian President Volodymyr Zelenskyy.

The capture of Mariupol would represent the Kremlin's biggest victory yet of the war in Ukraine. It would help Moscow secure more of the coastline, complete a land bridge between Russia and the Crimean Peninsula, which Russia seized in 2014, and enable Putin to shift more forces to the larger battle now underway for Ukraine's eastern industrial heartland.

By painting the mission in Mariupol a success, Putin may be seeking to take the focus off the plant, which has become a global symbol of defiance. Even without the plant, the Russians appear to have control of the rest of the city and its vital port, though that facility seems to have been extensively damaged.

"The Russian agenda now is not to capture these really difficult places where the Ukrainians can hold out in the urban centers, but to try and capture territory and also to encircle the Ukrainian forces and declare a huge victory," retired British Rear Adm. Chris Parry said.

Putin's order appeared to mean Russian forces intend to maintain the siege and wait for the defenders to surrender when they run out of food or ammunition. The bombardment of the plant could well continue.

Western nations, meanwhile, rushed to pour heavy weapons into Ukraine to help it counter the new offensive in the east.

U.S. President Joe Biden announced an additional $800 million in military assistance for Kyiv, including heavy artillery, 144,000 rounds of ammunition and drones.

But he also warned that the $13.6 billion approved last month by the U.S. Congress for military and humanitarian aid is "almost exhausted" and more will be needed.

Russia Defense Minister Sergei Shoigu estimated 2,000 Ukrainian troops remained at the steel plant. Ukrainian officials said about 1,000 civilians were also trapped there along with 500 wounded soldiers. Shoigu said the site was blocked off and predicted it could be taken in days.

"I consider the proposed storming of the industrial area pointless. I order to abort it," Putin responded, saying he was concerned about "preserving the life and health of our soldiers and officers."

"There is no need to climb into these catacombs and crawl underground through these industrial facilities," the Russian leader added. "Block off this industrial area so that not even a fly comes through."

All told, more than 100,000 people were believed trapped with little or no food, water, heat or medicine in Mariupol, which had a prewar population of about 430,000.

The city has seized worldwide attention as the scene of some of the worst suffering of the war, including deadly airstrikes on a maternity hospital and a theater.

German Foreign Minister Annalena Baerbock said her country and others are pressuring Russia to allow civilians out of Mariupol and to stop striking potential evacuation routes.

Four buses with civilians managed to escape the city on Wednesday after several unsuccessful attempts, according to Ukrainian Deputy Prime Minister Iryna Vereshchuk.

Ukraine has repeatedly accused Russia of launching attacks to block civilian evacuations from the city. On Thursday, at least two Russian attacks hit the city of Zaporizhzhia, a way station for people fleeing Mariupol, though no one was wounded, the regional governor said.

Parry called the decision about the steel plant a change in "operational approach" as Russia tries to learn from its failures in the 8-week-old conflict, which began with expectations of a lightning offensive that would crush Ukraine's outgunned and outnumbered forces and capture Kyiv. Instead, Moscow's troops became bogged down by unexpectedly tenacious resistance with ever-mounting casualties and retreated from the capital.

For weeks now, Russian officials have said capturing the Donbas, Ukraine's mostly Russian-speaking industrial east, is the war's main goal. Moscow's forces opened the new phase of the war this week - a deadly drive along a 300-mile (480-kilometer) front from the northeastern city of Kharkiv to the Azov Sea - to do just that.

"They've realized if they get sort of held up in these sort of really sticky areas like Mariupol, they're not going to cover the rest of the ground," Parry said.

In Luhansk, one of two regions that make up the Donbas, the governor said Russian forces control 80% of his region. Before Russia invaded on Feb. 24, the Kyiv government controlled 60% of Luhansk.

Britain's Defense Ministry said that Russia probably wants to demonstrate significant successes ahead of Victory Day on May 9, the proudest day on the Russian calendar, marking the defeat of Nazi Germany in World War II.

"This could affect how quickly and forcefully they attempt to conduct operations in the run-up to this date," the ministry said.

From the Associated Press