The governors of two Russian regions bordering Ukraine have said they inspected the construction of defence lines days after Ukrainian drone struck key military airfields.

The governor of the Kursk region, Roman Starovoyt, shared photos of pyramid-shaped concrete blocks that appear to be anti-tank fortifications.

His counterpart in the neighbouring Belgorod region, Vyacheslav Gladkov, on Tuesday reported inspecting local fortifications "to ensure the safety of all residents who live in the Belgorod region".

The region would be forming self-defence units, he added.

Russian officials say both regions have been repeatedly shelled by Ukrainian forces since President Vladimir Putin sent troops to the pro-Western country on February 24.

Following recent military defeats on the ground in Ukraine, they have stepped up the construction of defensive lines in border regions.

In its daily briefing on the Ukraine offensive, Britain's defence ministry said Wednesday these efforts were likely intended to "burnish patriotic feeling" among Russians.

But it also probably meant that some Russia decision-makers believed there was "a credible threat of invasion" from Ukraine, the ministry added.

In recent weeks, Russia has accused Ukraine of increasing attacks on its territory.

On Monday, Moscow blamed Kyiv for drone strikes at two key military airfields, both hundreds of kilometres away from Ukraine's border.