The International Military Tribunal (IMT) indictment charged certain acts which took place during the seige of Leningrad as war crimes:
(b) Murders and ill-treatments at places in the Eastern Countries and in the Soviet Union, other than in the camps referred to in (a) above, included), on various dates during the occupation by the German Armed Forces:
* * * * *
In the Leningrad region there were shot and tortured over 172,000 persons, including over 20,000 persons who were killed in the city of Leningrad by the barbarous artillery barrage and the bombings.
* * * * *
On the territory of the Soviet Union the Nazi conspirators destroyed or severely damaged 1,710 cities and more than 70,000 villages and hamlets, more than 6,000,000 buildings and made homeless about 25,000,000 persons.
Among the cities which suffered most destruction are Stalingrad, Sevastopol, Kiev, Minsk, Odessa, Smolensk, Novgorod, Pskov, Orel, Kharkov, Voronexh, Rostov-on-Don, Stalino, and Leningrad.
As is evident from an official memorandum of the German command, the Nazi conspirators planned the complete annihilation of entire Soviet cities.
In a completely secret order of the Chief of the Naval Staff (Staff Ia No; 1501/41, dated 29. IX. 1941) addressed only to Staff officers, it was said:
"The Fuehrer has decided to erase from the face of the earth St Petersburg. The existence of this large city will have no further interest after Soviet Russia is destroyed. Finland has also said that the existence of this city on her new border is not desirable from her point of view. The original request of the Navy \that docks, harbor, etc. necessary for the fleet be preserved—is known to the Supreme Commander of the Military Forces, but the basic principles of carrying out operations against St. Petersburg do not make it possible to satisfy this request.
"It is proposed to approach near to the city and to destroy it with the aid of an artillery barrage from weapons of different calibers and with long air attacks....
"The problem of the life of the population and the provisioning of them is a problem which cannot and must not be decided by us.
"In this war . . . we are not interested in preserving even a part of the
population of this large city."
http://forum.axishistory.com/viewtopic. ... 522#399522
The IMT judgment, on the other hand, only mentions Leningrad in passing, in its judgment against Alfred Jodl individually:
On 7 October 1941, Jodl signed an order that Hitler would not accept an offer of surrender of Leningrad or Moscow, but on the contrary he insisted that they be completely destroyed. He says this was done because the Germans were afraid those cities would be mined by the Russians as was Kiev. No surrender was ever offered.
IMT judgment against Alfred Jodl
http://forum.axishistory.com/viewtopic.php?t=71478
Refusal to grant quarter is a violation of both the laws and customs of war, but since the Soviets never offered to surrender the city, no quarter was asked. This remark in the IMT judgment pertains only to Jodl's willful intent to commit war crimes.
From the fact that this is the only mention of Leningrad in the IMT judgment, and the fact that the IMT did not convict any German government agencies or individual defendants on the charges of war crimes in connection with the siege, we can conclude that the IMT did not consider the siege itself as a war crime.
For an extensive discussion of the siege here in the H&WC section, see:
The Siege of Leningrad in German Documents
http://forum.axishistory.com/viewtopic.php?t=6860
Had Leningrad been razed to the ground after capture -- as the Germans intended -- that act would have been the war crime of spoliation, but as it happened the Germans were unable to conquer the city and the Nazi plans remained unrealized.