Former Soviet Embassy (now Embassy of Russia)

The former Embassy of the Soviet Union in Tokyo (旧ソビエト連邦大使館), now the Embassy of the Russian Federation (在日ロシア連邦大使館), stands at 2-1-1 Azabudai, Minato Ward, Tokyo. The embassy compound has occupied this site in the historic Mamiana (狸穴) neighborhood since 1928, when the Soviet diplomatic mission relocated here and constructed a two-story concrete building. The current main building was constructed by Obayashi Corporation in 1976. Due to its former address in Azabu-Mamiana-chō, the embassy was colloquially known as "Mamiana" (狸穴) in Japanese diplomatic circles.

The embassy holds profound significance in the closing days of World War II as the locus of the Soviet declaration of war against Japan. On April 5, 1945, the Soviet Union notified Japan of its intention not to renew the Soviet–Japanese Neutrality Pact (日ソ中立条約), originally signed on April 13, 1941, in Moscow by Foreign Minister Yōsuke Matsuoka and Soviet Foreign Minister Vyacheslav Molotov, with Joseph Stalin in attendance. The pact had been a cornerstone of Japan's northern defense strategy, freeing the Imperial Japanese Army from the threat of a two-front war.

At 5:00 p.m. Moscow time (11:00 p.m. Japan Standard Time) on August 8, 1945—just two days after the atomic bombing of Hiroshima—Molotov summoned Japanese Ambassador Naotake Satō to the Kremlin and read aloud the Soviet declaration of war. The declaration stated that Japan's rejection of the Potsdam Declaration justified Soviet intervention, citing the Allied request for Soviet participation. Molotov permitted Satō to transmit the declaration to Tokyo by ciphered telegram, but the Moscow central telegraph office, although it accepted the dispatch, never sent it on; the Japanese government learned of the declaration from Soviet news broadcasts at about 4 a.m. on August 9.

Molotov indicated that Soviet Ambassador Yakov Malik (who had served as ambassador to Japan since 1942) would simultaneously deliver the declaration to Foreign Minister Shigenori Tōgō in Tokyo. However, the formal meeting between Malik and Tōgō, held at the Soviet embassy's request, did not occur until August 10 at 11:15 a.m., when they met at the House of Peers VIP Room (貴族院貴賓室) rather than at the embassy itself. By that point, the Soviet invasion of Manchuria had already commenced at one minute past midnight Trans-Baikal time on August 9—barely an hour after the declaration—with simultaneous attacks on three fronts across Manchuria.

The Soviet entry into the war, combined with the atomic bombings of Hiroshima and Nagasaki, shattered Japan's last hope for a negotiated peace through Soviet mediation. The Supreme War Council (最高戦争指導会議), which had been attempting to use the Soviet Union as an intermediary for peace negotiations, was forced to confront the reality that unconditional surrender was the only option. Emperor Hirohito's "sacred decision" (聖断) to accept the Potsdam Declaration on August 14–15 was directly influenced by the dual shock of atomic weapons and Soviet entry.

A notable historical footnote: due to complications arising from the dissolution of the Soviet Union in 1991 and subsequent Russia-Ukraine relations affecting property registration, the embassy's land registration technically still bears the name of the Union of Soviet Socialist Republics (ソビエト社会主義共和国連邦) to this day, making it one of the last physical vestiges of the USSR in Japan.