Russian 14th army may strike from the back to support the main army, so they should be made toothless before the second wave of invasion, but Ukraine cannot attack 14th army without breaking relationships with Moldova, EU, UN, and NATO. However, Ukraine can exchange this problem (Transnistria) for another problem (Königsberg) to negate them both.
https://en.wikipedia.org/wiki/Russian_military_presence_in_T...
https://en.wikipedia.org/wiki/Cobasna_ammunition_depot