On 21 May, Amer asked Nasser to order the Straits of Tiran blockaded, a move Nasser believed Israel would use as a casus belli. Amer reassured him that the army was prepared for confrontation, but Nasser doubted Amer's assessment of the military's readiness. According to Nasser's vice president Zakaria Mohieddin, although "Amer had absolute authority over the armed forces, Nasser had his ways of knowing what was really going on". Moreover, Amer anticipated an impending Israeli attack and advocated a preemptive strike. Nasser refused the call upon determination that the air force lacked pilots and Amer's handpicked officers were incompetent. Still, Nasser concluded that if Israel attacked, Egypt's quantitative advantage in manpower and arms could stave off Israeli forces for at least two weeks, allowing for diplomacy towards a ceasefire. Towards the end of May, Nasser increasingly exchanged his positions of deterrence for deference to the inevitability of war, under increased pressure to act by both the general Arab populace and various Arab governments. On 26 May Nasser declared, "our basic objective will be to destroy Israel". On 30 May, King Hussein committed Jordan in an alliance with Egypt and Syria.

What thoroughfare did Amir want Nasser to block?