Providing English translations and expanding upon the answer by @James Slides referencing the brief exchanges of fire between forces from the German 1st Mountain Division and elements of the Soviet Volotchitsky Army Group near Lviv in 1939.
September 19th, 1939, near Lviv
At 5.00, the commander of the 24th LTBR Colonel P.S. Fotchenkov
ordered the reconnaissance battalion to remain in the city, but to
close the exits on the eastern outskirts of Lviv. A separate tank
brigade commander ordered to go to the eastern outskirts of Vinniki
(the vicinity of the city of Lviv). Captain Shurenkov, the commander
of the 2nd unit, contact the Polish headquarters and call the head of
the Lviv garrison to negotiate the surrender of the city.
Two armored vehicles sent from Lviv eastward along another road
towards the Soviet troops marching towards the city were suddenly
subjected to shelling. The commanders thought it was Polish troops and
entered the battle, firing from 45-mm cannons and machine guns. As it
turned out later, the crews of the armored communications delegates
knocked out two anti-tank guns and killed one German officer and four
soldiers. Two Soviet armored vehicles with their glorious crews fought
to the last covered in fire and burned. This was learned from the
representatives from the headquarters of the 1st German Mountain
Infantry Division and the 137th German Regiment.
...and later the same day.
At 8.30. Lviv. The Germans unexpectedly launched an attack on the western and southern outskirts of the city. Polish troops took the battle, and
Soviet tanks and armored vehicles of the 24th LTBR reconnaissance
battalion were between the warring parties. The brigade commander
Colonel Fotchenkov sent an armored vehicle with the white flag to the
Germans. Soviet commanders in tanks and armored vehicles gave signals
in red and white flags, but the fire on them from both sides did not
stop. Having exhausted peaceful methods of ceasefire, Soviet tankmen
opened fire on the enemy. At the same time, 3 anti-tank guns were
killed [of] the Germans, 3 officers were killed (two of them were
major), and 9 soldiers were wounded. In the 24th brigade, 2 armored
vehicles and 1 tank were killed, 3 people were killed and 4 people
were injured. Seeing their losses, the Germans stopped artillery fire.
The above is an English translation from Russian language Wikipedia
Meltiukhov M.I., Soviet-Polish War. Military-political confrontation 1918-1939 Part 3. September 1939 War from the West - M., 2001. Chapters: Forces of the parties; Polish campaign of the red army: September 17-21; Moscow-Berlin. See “Forces of the parties. Table 27. Grouping of Soviet troops by September 17, 1939 ”; “The Polish Red Army Campaign: September 17-21”; "Moscow-Berlin"; "The Polish campaign of the red army: September 22 - October 1."
A personal account of the incident
"Then, on the morning of September 17, the 24th tank brigade of Colonel
P.S. Fotchenkov, which included a tank reconnaissance battalion under
my command, along with other parts of the Kiev Special Military
District crossed the border in the Ternopil direction. The battalion
operated in the advance detachment. By the evening of the same day we
reached Ternopil, and on the night of September 19 entered Lviv. The
population greeted the Red Army with glee. Our mood was elated: after
all, we carried out a fair liberation mission. Our forward detachment
continued to advance rapidly toward the demarcation line. Suddenly, we
saw German tanks rushing towards Lviv, infantry and artillery. It
alerted. After all, the demarcation line established in advance passed
much to the west. The Germans could not have been unaware that the
Polish army of General Langer, which had been defending Lviv from the
west, had laid down their arms. Nevertheless, the Germans were clearly
in a hurry to break into the city, apparently hoping to get ahead of
our main forces. What to do? Give way and let them go to Lviv? Not. We
must block the way! At my command, the battalion turned around. We
made it clear to the Germans that they should not move to the
territory occupied by the Soviet troops, but they opened fire on our
tanks. And again the question: how to respond to a clear provocation?
I made a decision - to open fire. Having taken an advantageous
position, the tankers of the battalion fired several salvos from
cannons. Our fire turned out to be quite accurate: several German
guns, put forward for direct fire, were silent, several soldiers and
officers were killed and wounded. Not without losses and with us.
Political instructor Vasily Poznyakov died, two armored vehicles
burned down. The next day, the Germans apologized and regretted the
clash. They tried to explain everything with what the Soviet troops
mistook for the Polish defending Lviv. We had to listen and accept
these apologies. However, we felt in our hearts - it was very
important for the Nazis to conduct reconnaissance of our strength, to
test the ability to resist. Well, the first test could not reassure
them ... In those days, we had several so-called friendly meetings.
First, about 20 German officers arrived at our place. The brigade
commander Colonel Fotchenkov received them on the outskirts of Lviv -
in Vinniki. This meeting was attended by many commanders and political
workers of our brigade. I also happened to be there. We accepted the
guests according to all the rules. They led them to the location of
the unit, showed military equipment. The guests smiled and
complimented us. But their excessive curiosity irritated and alarmed
us. They were especially interested in tanks. They looked around from
the outside, looked into the hatches, the towers, tried to learn as
much as possible about the armor, weapons, about all the tactical and
technical data of our machines."
From the memoirs of the chief of staff and then the commander (in 1941) of the 63rd Tank Regiment of the 32nd Tank Division A. V. Egorova. (Sourced from LiveJournal.)