At the same time, and unknown to the Israelis, the Soviet Union mounted a disinformation campaign pushing Egypt to join Syria against Israel. At that time, the Soviets were providing military and economic aid to both Syria and Egypt. On May 13, 1967 a Soviet parliamentary delegation visited Cairo and informed the Egyptian leaders that Israel had concentrated eleven to thirteen brigades along the Syrian border in preparation for an assault within a few days, with the intention of overthrowing the revolutionary Syrian Government. This was a complete fabrication designed by the Soviets to destabilize the Middle East. Similar false information may have been given to Egypt by the Soviets as early as May 2. The build up and aggressive intent were denied by Israel. UN Secretary General U Thant reported that UNTSO observers on the Syrian border:... have verified the absence of troop concentrations and absence of noteworthy military movements on both sides of the [Syrian] line.
Nasser probably correctly interpreted the Soviet information as an indication to him that the time was ripe for an attack on Israel and that he had their backing. With the United States deeply distracted by the War in Vietnam, the Soviets had reason to think there would be no US intervention. Nassar then abandoned his former cautious policy and took the lead for new aggression against Israel. Syria and Iraq eagerly joined Egypt's preparations, increasing the momentum toward war.