According to the
travel advice for Russia issued by the UK Foreign and Commonwealth Office, it appears that third-country nationals (who aren't Belarusian/Russian citizens) are still able to travel directly between Belarus and Russia by air and by train (but not by road):
Travelling between Russia and Belarus
The Russian government has informed the UK government that there are no legal grounds to allow third country nationals, including British nationals, to cross between Russia and Belarus by road. If you’re planning on entering Russia by road, you’ll need to take an alternative route through a different country. The UK government isn’t aware of any difficulties encountered by British nationals when travelling between Russia and Belarus by air or rail, but you should make sure that you have all the necessary visas required for the duration of your travel.
Smartraveller advice for Russia from the Australian Government Department of Foreign Affairs and Trade also suggests that the restriction only applies to land crossings:
You might not be permitted to enter Russia from Belarus if travelling by car or bus (including tour-operated buses) as some border crossings are designated for local residents only. This also applies to the main European Highway E30 (which crosses the border of Russia/Belarus closest to Smolensk). It is unclear at this stage which land border crossings, if any, are accessible to Australian travellers. If you intend on crossing into Russia from Belarus, enquire with the Embassy of the Russian Federation in Australia.
Also, according to an article from
Belarus News, it appears that the Belarusian Government is quite keen to restore the ability of third-country nationals to travel directly by road between Belarus and Russia as soon as possible. Another
Belarus News article published yesterday suggests that there has been a significant drop in the number of transit visitors (particularly EU citizens).