Ukrainian defenders in Mariupol are tying up a 'significant' amount of Russian forces that are needed elsewhere for Putin's invasion, UK says

• Ukraine's defense of Mariupol is bogging down 'significant' numbers of Russian troops and equipment.
• Besieged Mariupol has remained in Ukrainian control, despite weeks of widespread shelling.

Ukrainian defenders in besieged Mariupol are tying up a "significant" amount of Russian troops and equipment that will soon be needed elsewhere, UK intelligence said on Thursday.

Russian forces are preparing for a renewed offensive in Ukraine's eastern Donbas region, the UK's Ministry of Defense tweeted, and will need a large number of troops to do so.

But President Vladimir Putin's troops may be limited by the ongoing campaign to capture Mariupol, which has remained under Ukrainian control despite constant bombardment by Russian forces.

The strategic southern port city has been surrounded for weeks by the Russian military, which has launched a devastating bombing campaign against the city. Russia has targeted civilian areas, including schools, shelters, theaters, and hospitals.

Earlier this week, Ukrainian President Volodymyr Zelenskyy said "tens of thousands" of Ukrainian civilians could be dead in Mariupol.

Western and NATO officials have said Russian troops repositioned away from the country's northern region to focus on the Donbas after failing to capture the capital city Kyiv.

UK intelligence said Russia is trying to concentrate its forces ahead of the offensive and using "widespread" shelling tactics, adding that the upcoming military campaign would require "significant force levels."

Satellite imagery and videos show Russian forces and military convoys headed to the region.

"It could be a big war in Donbas — like the world has not seen in hundreds of years," Zelenskyy warned.

Ukraine warned residents of the region to evacuate ahead of the upcoming offensive. Last week, dozens were killed in a Russian rocket strike on a train station in Kramatorsk as civilians tried to flee the area.