For years after the Six-Day War, the consensus view among historians was that it was set off as the result of a series of accidents. However, the declassification in 2015 of documents from the Israel Defence Forces archives at Israel's Ministry of Defence show that Israel's concern over protecting against the elimination of its nuclear reactor in Dimona, which it had begun constructing in 1958, played a far greater role in Israel’s decision to launch a pre-emptive strike than was previously proven.  

These declassified documents reveal that in a meeting of government ministers and IDF top brass on June 2,1967 the IDF expressed deep concern that the Egyptians would launch an air strike on Israel's nuclear reactor in Dimona if Israel didn't launch a pre-emptive strike and crush Egypt's air force. "http://www.haaretz.com/june-67-idf-feared-egyptian-strike-on-dimona-1.322776

Had Israel's nuclear reactor at Dimona been destroyed, there would have been radioactive contamination over all of Israel. Given this nuclear context, Chief of Staff Yitzhak Rabin’s nervous breakdown prior to the war, which was withheld from the Israeli public, is understandable. 

 Although declassified documents from 1967 refer to Egyptian warplanes which invaded Israel's airspace to photograph the nuclear reactor on Dimona,  Ginor and Remez argue quite persuasively in their book that the planes were not in fact Egyptian, but rather Russian MIG 25's, (aka Foxbats), flown by Russian pilots.  The  Foxbat planes directly overflew the Dimona reactor at least twice on May 17 and May 26. This is a critical point. If the Soviets provocatively flew Foxbats over Israel’s most sensitive site while the Israeli army was mobilized, conventional analysis that the Soviets acted to avert a crisis rather than stoke it is wrong.  Remez and Ginor contend that the Foxbat planes flew too high and too fast for Israel’s Hawk anti-aircraft batteries and Mirage III fighters to intercept or shoot them down.

Anticipation of war spurs Israel to produce nuclear bomb 

It is likely that the Egyptians and/or Soviets believed that Israel could be stopped from reaching nuclear status by military action.  According to Avner Cohen in "Hataboo", the threat of war spurred Israel to make a rudimentary nuclear bomb operational. Cohen writes, " As claimed in foreign publications, shortly before the Six-Day War, Israel had obtained most of the components for nuclear capability without possessing the weapons themselves. During the period of high alert before the war, considering the anxieties about a worst case [referring to preparations for an attack with unconventional weapons and particularly poison gas], Israel by a concentrated effort, improvised a usable weapons system out of its capabilities...Foreign sources spoke of two nuclear devices made operational." (Foxbats Over Dimona, p.139).

The Ginor-Remez Theory

In their ground breaking  book,  Ginor and Gideon Remez  assert that having received information about Israel's progress toward nuclear arms, the Soviets aimed to draw Israel into a confrontation, which would have given the Soviets a pretext to strike Dimona. Rather than strike Israel out of the blue, the Soviets developed a plan to lure Israel into attacking Egypt and Syria, which would in turn provide cover and political justification for a retaliatory strike on Dimona. Israel would be branded as the aggressor, the US would disapprove of Israel's actions and not intervene on Israel's behalf, and a joint Arab-Soviet counterattack would follow. "Israel would be attacked on an issue with which it was at serious odds with the United States" in that Washington "was almost as apprehensive as Moscow about the prospect of Israel acquiring atomic weapons." 

The Egyptians and Soviets believed that the Egyptian army would halt the initial Israeli attack in the Sinai, and follow with a counter-strike that would include Dimona. Israel would be wiped out.

Israel’s opening air strike against the Egyptian Air Force on the morning of June 5 was so devastating that by 11 a.m., there were no functioning Egyptian air bases. By the afternoon of the first day, half of Syria’s Air Force and the entire Jordanian Air Force were destroyed. Ginor and Remez argue that without air cover or air bases, the Soviets dropped their plan to remake the Middle East, and covered their tracks to minimize their role in the fiasco. The authors cite former Soviet Foreign Ministry Middle East Specialist Oleg Ginevsky, who said  “Only Israel’s sudden blow on the Egyptian airfields and Egypt’s rout in this six day war saved Dimona from annihilation and Israel from radioactive contamination.”

In short,  Foxbats over Dimona: The Soviets' Nuclear Gamble in the Six-Day War is a worthwhile read for anyone interested in learning about the history of the Six Day War.

Finally, Ginor and Remez found a critical piece of  evidence after their book was published.   The Soviets themselves inadvertantly confirmed in 2006 that they flew Foxbat planes over Israel in 1967, as discussed in David Horowitz’s article in the Jerusalem Post, "Russia confirms Soviet sorties over Dimona in '67.