The Israeli cabinet met on May 23 and decided to launch an attack if the Straits of Tiran were not re-opened by May 25. Following an approach from United States Under Secretary of State for Political Affairs Eugene Rostow to allow time for the negotiation of a nonviolent solution, Israel agreed to a delay of ten days to two weeks. UN Secretary General, U Thant, visited Cairo for mediation and recommended a moratorium in the Straits of Tiran and a renewed diplomatic effort to solve the crisis. Egypt agreed, but Israel rejected these proposals. Nasser's concessions did not necessarily suggest that he was making a concerted effort to avoid war. The decision benefited him both politically and strategically. Agreeing to diplomacy helped garner international political support. Moreover, every delay gave Egypt time to complete its own military preparations and coordinate with the other Arab forces. Also, Israel's rejection did not necessarily demonstrate a desire for war so much as it demonstrated the urgency it felt the situation warranted. Israel felt it could not afford to sustain total mobilization for long. Caught up in Arab enthusiasm for military action and encouraged by the lack of response to the closure of the Straits, Egyptian Field Marshal Amer planned for initiating an attack on Israel in late May. He told one of his generals that "This time we will be the ones to start the war." This was counter to Nasser's strategy of pushing Israel to start the war. Historian Michael Oren states that Egyptian sources are divided over why Nasser did not veto Amer's plan. Oren suggests that "Nasser was apprised of [the plan] but lacked the political strength to override Amer's order. Also, the preparation of an Egyptian invasion of Israel had certain advantages for Nasser"

The U.S. also tried to mediate, and Nasser agreed to send his vice-president to Washington to explore a diplomatic settlement. Most American diplomats who worked in the Middle East were sympathetic to Nasser's views on the Straits, with several of them arguing that the U.S. should ignore both its on-the-record promises to Israel regarding the Straits being open and international law; a few diplomats who were not as impressed by threats from Arab nations advised the Johnson Administration to back the flotilla option as a "show of force" that would forestall war from breaking out. The meeting did not happen because Israel launched its offensive. Some analysts suggest that Nasser took actions aimed at reaping political gains, which he knew carried a high risk of precipitating military hostilities. On this view, Nasser's willingness to take such risks was based on his fundamental underestimation of Israel's capacity for independent and effective military action.

On May 25, 1967, Israeli Foreign Minister Abba Eban landed in Washington “with instructions to discuss American plans to re-open the Strait of Tiran”. As soon as he arrived, he was given new instructions in a cable from the Israeli government. The cable said that Israel had learned of an imminent Egyptian attack, which overshadowed the blockade. No longer was he to emphasize the strait issue; he was instructed to ‘inform the highest authorities of this new threat and to request an official statement from the United States that an attack on Israel would be viewed as an attack on the United States.”According to most sources, including those involved, the new instructions were sent at the instigation of Chief of Staff Yitzhak Rabin, who was eager to force an American decision – either Johnson would have to commit to specific American action then, or Israel would be free to act on its own. Historian Michael Oren explains Eban's reaction to the new instructions: "Eban was livid. Unconvinced that Nasser was either determined or even able to attack, he now saw Israelis inflating the Egyptian threat - and flaunting their weakness - in order to extract a pledge that the President, Congress-bound, could never make." He described the cable as an ' act of momentous irresponsibility... eccentric...' which 'lacked wisdom, veracity and tactical understanding,' and later came to the conclusion that the genesis of the cable was Rabin's indecisive state of mind.

Despite his own skepticism, Eban followed his instructions during his first meeting with Secretary Rusk, Under Secretary Rostow, and Assistant Secretary Lucius Battle. American intelligence experts spent the night analyzing each of the Israeli claims. On May 26, Eban met with United States Secretary of State Dean Rusk, Defense Secretary Robert McNamara, and finally with President Lyndon B. Johnson. In a memo to the President, Rusk rejected the claim of an Egyptian and Syrian attack being imminent, plainly stating "our intelligence does not confirm the Israeli estimate". According to declassified documents from the Johnson Presidential Library, President Johnson and other top officials in the administration did not believe war between Israel and its neighbors was necessary or inevitable. "All of our intelligence people are unanimous that if the UAR attacks, you will whip hell out of them", Johnson told Eban during a visit to the White House on May 26. This assertion was made in accordance with a CIA assessment that Israel could “defend successfully against simultaneous Arab attacks on all fronts or hold on any three fronts while mounting successfully a major offensive on the fourth." Consequently, Johnson declined to airlift special military supplies to Israel or even to publicly support it. Eban left the White House distraught.

In a lecture given in 2002, Oren said, "Johnson sat around with his advisors and said, ‘What if their intelligence sources are better than ours?’ Johnson decided to fire off a Hotline message to his counterpart in the Kremlin, Alexei Kosygin, in which he said, ‘We've heard from the Israelis, but we can't corroborate it, that your proxies in the Middle East, the Egyptians, plan to launch an attack against Israel in the next 48 hours. If you don't want to start a global crisis, prevent them from doing that.’ At 2:30 a.m. on May 27, Soviet Ambassador to Egypt Dimitri Pojidaev knocked on Nasser's door and read him a personal letter from Kosygin in which he said, ‘We don't want Egypt to be blamed for starting a war in the Middle East. If you launch that attack, we cannot support you.’ Amer consulted his sources in the Kremlin, and they corroborated the substance of Kosygin's message. Despondent, Amer told the commander of Egypt's air force, Major General Mahmud Sidqi, that the operation was cancelled." According to then Egyptian Vice-President Hussein el-Shafei, as soon as Nasser knew what Amer planned, he cancelled the operation.

On 30 May, Nasser responded to Johnson's request of 11 days earlier and agreed to send his Vice President, Zakkariya Muhieddin, to Washington on June 7 to explore a diplomatic settlement in "precisely the opening the White House had sought". Historian Michael Oren writes that Rusk was "mad as hell" and that Johnson later wrote "I have never concealed my regret that Israel decided to move when it did".

Within Israel's political leadership, it was decided that if the US would not act, and if the UN could not act, then Israel would have to act. On 1 June, Moshe Dayan was made Israeli Defense Minister, and on June 3 the Johnson administration gave an ambiguous statement; Israel continued to prepare for war. Israel's attack against Egypt on June 5 began what would later be dubbed the Six-Day War. According to Martin van Creveld, the IDF pressed for war: "...the concept of 'defensible borders' was not even part of the IDFs own vocabulary. Anyone who will look for it in the military literature of the time will do so in vain. Instead, Israel's commanders based their thought on the 1948 war and, especially, their 1956 triumph over the Egyptians in which, from then Chief of Staff Dayan down, they had gained their spurs. When the 1967 crisis broke they felt certain of their ability to win a 'decisive, quick and elegant' victory, as one of their number, General Haim Bar Lev, put it, and pressed the government to start the war as soon as possible". Some of Israel's political leaders, however, hoped for a diplomatic solution.