On 13 May 1967 Nasser received a Soviet intelligence report which claimed that Israel was massing troops on Syria's border. Nasser verified that the report was false, but still told his people that Israel troops are placed on Syria's border. Subsequently, he took three successive steps that made war virtually inevitable: On 14 May he deployed his troops in Sinai near the border with Israel, on 19 May expelled the UN peacekeepers stationed in the Sinai Peninsula border with Israel, and on 23 May closed the Straits of Tiran to Israeli bound shipping., although he knew that it would be considered a Casus belli by Israel. 90% of Israeli oil passed through the Straits of Tiran. Oil tankers that were due to pass through the straits were delayed.