Unfortunately (at least for Germany), the answer is NO. The move you are describing, seizing Moscow with 1 tank–while it is occupied by USSR troops or not–is considered a COMBAT MOVE since you are moving your unit(s) into a territory you or your allie(s) do not currently own. Since the Karelia battle has already been fought, that means the COMBAT portion of your turn is over, and NON-COMBAT MOVEMENT begins. On NON-COMBAT MOVEMENT you are not allowed to move offensively (that is; into enemy territory). Therefore, your ARM in Eastern Europe IS allowed to move, but not into any enemy-held territory.
One of my friends (who is an ex-football player) always refers to the COMBAT MOVE portion of the turn as “OFFENSE MOVE”, while the NONCOMBAT MOVE he calls “DEFENSE MOVE”. While not technically correct, this nomenclature, I’ve found, can sometimes be helpful for determining whether a move is legal or not. Basically, anything “OFFENSIVE” in nature is not allowed in NonCombat–that is anything after the COMBAT is over.
The only exception is if you have “rockets”–then you can launch a rocket attack at ANY TIME during your move. This is the only “offensive-type” move allowed after COMBAT.
Ozone27