Nasser began massing his troops 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.
Nasser declared the Straits closed to Israeli shipping on May 22–23. The following day, at Jordan's invitation, the Iraqi army began deploying troops and armored units in Jordan.
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.
In January 1964 an Arab League summit meeting convened in Cairo, claimed that the diversion of the Jordan waters by Israel multiplies the dangers to Arab existence and decided to deprive Israel of 35% of the National Water Carrier capacity, by a diversion of the Jordan River headwaters (both the Hasbani and the Banias tributaries) to the Yarmouk River, although the scheme was only marginally feasible, it was technically difficult and expensive.
The following year, the Arab states began construction of the Headwater Diversion Plan, which, once completed, would divert the waters of the Banias Stream before the water entered Israel and the Sea of Galilee, to flow instead into a dam at Mukhaiba for use by Jordan and Syria, and divert the waters of the Hasbani into the Litani River in Lebanon.Tension escalated, with both sides' armies mobilising.Less than a month later, Israel launched a surprise strike which began the Six-Day War.Moshe Dayan, the Israeli defense minister at the time of the Six Day War, recounted in a 1976 interview that Israeli policy in the Demilitarized Zone between 19 was "to seize some territory and hold it until the enemy despairs and gives it to us", thus changing "the lines of the ceasefire accord with military actions that were less than a war".Publicly, Syria claimed that the escalating conflict was the result of Israel attempting to increase tension in order to justify a large-scale military operation against Syria, and to expand its occupation of the Demilitarized Zone by dispossessing the remaining Arab farmers.Arab nationalists, led by Egyptian President Gamal Abdel Nasser, continued to be hostile to Israel's existence and made grave threats against its Jewish population.By the mid-1960s, relations between Israel and its Arab neighbors had deteriorated to the extent that a number of border clashes had taken place.Under no circumstances would Israel agree to the stationing of UN forces on its territory or in any area it occupied.After the 1956 war, Egypt agreed to the stationing of a UN peacekeeping force in the Sinai, the United Nations Emergency Force, to keep that border region demilitarized, and prevent Palestinian fedayeen guerrillas from crossing the border into Israel.The origins of the Six-Day War, which was fought between June 5 and June 10, 1967, by Israel and the neighboring states of Egypt (known then as the United Arab Republic, UAR), Jordan, and Syria, include both longstanding and immediate issues.At the time of the Six-Day War, the earlier foundation of Israel, the resulting Palestinian refugee issue, and Israel's participation in the invasion of Egypt during the Suez crisis of 1956 continued to be significant grievances for the Arab world.