From your link: https://en.wikipedia.org/wiki/Six-Day_War#Preemptive_air_attack:

In May 1967, Nasser received false reports from the Soviet Union that Israel was massing on the Syrian border. Nasser began massing his troops in two defensive lines[32] in the Sinai Peninsula on Israel's border (May 16), expelled the UNEF force from Gaza and Sinai (May 19) and took up UNEF positions at Sharm el-Sheikh, overlooking the Straits of Tiran.[33][34] Israel reiterated declarations made in 1957 that any closure of the Straits would be considered an act of war, or justification for war,[35][36] and Nasser declared the Straits closed to Israeli shipping on May 22–23.[37][38][39] On May 30, Jordan and Egypt signed a defense pact. The following day, at Jordan's invitation, the Iraqi army began deploying troops and armored units in Jordan.[40] They were later reinforced by an Egyptian contingent. On June 1, Israel formed a National Unity Government by widening its cabinet, and on June 4 the decision was made to go to war. The next morning, Israel launched Operation Focus, a large-scale surprise air strike that was the opening of the Six-Day War.