Britain's defense ministry says Russian authorities may be considering a withdrawal of their forces from the city of Kherson in southern Ukraine as the country's forces step up their counteroffensive.

The ministry published its latest intelligence update on Thursday.

It referred to a remark made on Tuesday by Russia's new military commander Sergey Surovikin, acknowledging that the situation in the Kherson region is difficult.

The update said the commander's "announcement highlighting negative news about 'the special military operation' is highly unusual."

It also said, "It likely indicates that the Russian authorities are seriously considering a major withdrawal of their forces from the area west of the Dnipro river," where the city of Kherson lies.

The ministry pointed out, however, that a key challenge of any Russian withdrawal operation would be extracting troops and their equipment across the 1,000-meter-wide river. It said, "Russia would highly likely rely heavily on a temporary barge bridge" as "all the permanent bridges" over the river have been severely damaged.

Also on Wednesday, the US-based think tank Institute for the Study of War said, "Russian authorities are likely setting information conditions to justify planned Russian retreats and significant territorial losses."

The think tank also commented on Russian President Vladimir Putin's introduction of martial law in four unilaterally annexed regions of Ukraine and enhancing local governments' authority in Russia.

It said the "declaration of martial law readiness is largely legal theater meant to legitimize activities the Russian military needs to undertake or is already undertaking while creating a framework for future mobilization and domestic restrictions."

The Ukrainian forces are believed to be preparing to advance to the region's main city of Kherson.

The pro-Russian head of the Ukrainian region said on Wednesday that residents are being evacuated to Russia, and that administrative bodies are also being moved to safer places.