By mid-June, after unsuccessful economic blockade of Lithuania, the Soviets started negotiations with Lithuania and the other two Baltic republics. The Soviets had a bigger challenge elsewhere, as the Russian federal republic proclaimed sovereignty in June. Simultaneously the Baltic republics also started to negotiate directly with the Russian federal republic. After the failed negotiations the Soviets made a dramatic but failed attempt to break the deadlock and sent in military troops killing twenty and injuring hundreds of civilians in what became known as the "Vilnius massacre" and "The Barricades" in Latvia during January 1991. In August 1991, the hard-line members attempted to take control of the Soviet Union. A day after the coup on 21 August, the Estonians proclaimed full independence, after an 1991 Estonian independence referendum was held in Estonia on 3 March 1991, alongside a similar referendum in Latvia the same month. It was approved by 78.4% of voters with an 82.9% turnout. Independence was restored by the Estonian Supreme Council on the night of 20 August. The Latvian parliament made similar a declaration on the same day. The coup failed but the collapse of the Soviet Union became unavoidable. After the coup collapsed, the Soviet government recognised the independence of all three Baltic states on 6 September 1991.