KYIV: Moscow ordered troops to withdraw from near the strategic southern Ukrainian city of Kherson in a major setback as a top U.S. general estimated Russia has suffered more than 100,000 killed or wounded since invading its neighbour in February.

Defence Minister Sergei Shoigu on Wednesday announced Russian forces would retreat from the west bank of the Dnipro River near Kherson in what could be a turning point in the war.

Ukraine reacted with caution, noting some Russian forces remained in Kherson and reinforcements were being sent to the region.

"They are moving out but not as much as would be taking place if it was a full pullout or regrouping," Oleksiy Arestovych, adviser to President Volodymyr Zelenskiy, said in a video posted online on Wednesday night.

Russian forces were destroying bridges as they left and mining roads, Arestovych said.

"For the moment, we don't know their intentions - will they engage in fighting with us and will they try to hold the city of Kherson? They are moving very slowly," he said.

Kherson city was the only regional capital Russia captured after the invasion and it has been the focus of a Ukrainian counter-offensive. The city controls the only land route to the Crimea peninsula that Russia annexed in 2014 and the mouth of the Dnipro river that bisects Ukraine.

Russian-installed officials have been evacuating tens of thousands of civilians from Kherson in recent weeks.

Ukrainian military analyst Yuri Butusov said the Ukrainian army's use of U.S.-supplied high mobility artillery rocket systems (HIMARS) had made Dnipro river crossings so dangerous that "the defence of Russian positions here has become impossible".

"But let's be clear. The Russian forces will take up defensive positions and it will be able to carry out new attacks. It will be able to maintain its positions on the east bank for a time," Butusiov said in a YouTube video.

CASUALTIES

America's top general estimated on Wednesday that Russia's military had suffered more than 100,000 of its soldiers killed or wounded, and added Kyiv's armed forces "probably" suffered a similar level of casualties. About 40,000 Ukrainian civilians were also probably killed, he said.

The estimates could not be independently confirmed by Reuters. General Mark Milley, speaking to the Economic Club in New York, did not say how he calculated those estimates.

Milley said nitial indicators suggested Russia was following through with its withdrawal from Kherson. But he cautioned that it could take time to complete.

In televised comments, Russian General Sergei Surovikin, in overall command of the war, reported to Shoigu that it was no longer possible to supply Kherson city. He said he proposed to take up defensive lines on the eastern bank of the Dnipro River.

Shoigu told Surovikin: "I agree with your conclusions and proposals. For us, the life and health of Russian servicemen is always a priority. We must also take into account the threats to the civilian population.

"Proceed with the withdrawal of troops and take all measures to ensure the safe transfer of personnel, weapons and equipment across the Dnipro River."

'STEP BY STEP'

Ukrainian forces were strengthening their positions "step by step" in the south, Zelenskiy said in a Wednesday night address that metntioned Kherson just once, and warned that "the enemy will make no gifts to us."

U.S. President Joe Biden said Moscow's order to withdraw from Kherson showed there were "some real problems with the Russian military."

Biden said he hopes Democrats and Republicans can continue the bipartisan approach of confronting Russia's aggression in Ukraine after Tuesday's midterm elections, in which his Democratic Party performed better than expected.

SHELLING IN SOUTH

A regular evening statement by the Ukrainian military on Wednesday made no direct reference to Kherson region or its capital. Russian forces shelled more than 25 towns and villages on the southern front, it said.

Ukrainian legislator David Arakhamia, who led Kyiv's delegation to peace talks early in Russia's invasion, said however, that a military operation in the Kherson region was under way.

He described the Russians' situation as critical and said, "Sooner or later, they will either leave Kherson, Donetsk, Luhansk and Sevastopol (in Crimea) or be destroyed."

But the Ukrainians may face numerous booby traps in Kherson and could be targeted by intense Russian artillery barrages.

NATO Secretary General Jens Stoltenberg, speaking to Sky News during a visit to London, welcomed the news on Kherson but also warned that "Russia can still inflict a lot of damage."

Compounding the sense of Russian disarray in Kherson, Moscow's number two official there, Kirill Stremousov, was killed on Wednesday in what Moscow said was a car crash.

Russia's leading war hawks on Wednesday endorsed the decision to abandon Kherson city, putting a brave face on one of Moscow's most humiliating retreats.

"After weighing all the pros and cons, General Surovikin made the difficult but right choice between senseless sacrifices for the sake of loud statements and saving the priceless lives of soldiers," said Ramzan Kadyrov, the Chechen leader who has frequently urged a more aggressive approach to the war.

(Reporting by Reuters bureaux; Writing by Grant McCool and Michael Perry; Editing by Cynthia Osterman & Simon Cameron-Moore)