The Soviet Union played a crucial role in arming the Arab states and instigating the Six-Day War.
Initially supportive of Israel at the time of its founding, by the early 1950s the Soviets no longer regarded the Zionist state as useful for extending their influence into the Middle East. Transferring their support to Arab side, the Soviets took on the role of armorer for both Syria and Egypt, supplying them with modern tanks, aircraft and later missiles. The Egyptian and Syrian armed forces primarily used Soviet weapons during the 1967 war and employed tactics developed by the Soviets.
The Soviet Union exerted a troublesome influence on the events leading up to the war by feeding Arab suspicions about Israel. This culminated in the delivery to the Syrians and Egyptians of a false alert on May 13 that Israel had massed troops near the Israeli-Syrian border in preparation for an attack on Syria.
Although it is not clear that the Soviets actually desired a war, a recent book by Gideon Remez and Isabella Ginor, Foxbats over Dimona: The Soviets' Nuclear Gamble in the Six-Day War, makes the controversial contention that the Soviet Union intentionally sparked the war in order to justify an attack against Israel's nuclear facility in Dimona. Israel's rapid and overwhelming success undermined the plan, the authors argue.
After the war the Soviets rapidly made up the equipment losses suffered by the Syrians and Egyptians and increased their involvement in Egypt’s anti-aircraft defenses.
Israel’s victory in the Six-Day War had an enormous impact on the Jewish population in the Soviet Union and helped set in motion the Jewish exodus from the Communist regime. As famed refusenik, Natan Sharansky reminisced,
we knew all too well the anti-Semitic stereotypes about greed, parasitism, and cowardice — but about what Judaism stood for, we knew nothing.
That was before 1967. In the months leading up to the war, animosity towards us reached a fever pitch. Then, in six dramatic days, everything changed for us. The call that went up from Jerusalem, “The Temple Mount is in our hands,” penetrated the Iron Curtain and forged an almost mystic link with our people. And while we had no idea what the Temple Mount was, we did know that the fact that it was in our hands had won us respect. Like a cry from our distant past, it told us that we were no longer displaced and isolated. We belonged to something, even if we did not yet know what, or why. Of course, we still suffered from anti-Semitism, but even that assumed a new character. Jews were no longer cowards. Instinctively, and without any real connection to Judaism, we became Zionists. We knew that somewhere there was a country that called us its children, and this knowledge filled us with pride.
“The Political Legacy of Theodore Herzl,” Natan Sharansky, Azure, Summer 2005
"Soviets Engineered the Six Day War," Jerusalem Post, May 16, 2007