梭发那·富马亲王
With the FAN offering steadily less reliable support to the Royalists, and the communists on the offensive, neutralist Prime Minister Souvanna Phouma convened a conference on the Plain of Jars on 17 April 1964. Failing in his attempt to calm or quell the three-sided conflict, and discouraged by his failure, Souvanna Phouma returned to Vientiane prepared to resign. However, on the night of 18 April, General Siho Lamphouthacoul led the National Police in a coup. General Kouprasith Abhay, who commanded the Royalist troops in the capital, consented to the coup. Without opposition, Siho's "Bataillon Special 33" (Special Battalion 33) conquered the capital's governmental infrastructure. The following morning, coup troops arrested Souvanna Phouma and about 15 other important personages; the detainees were a mixed bag of Frenchmen, Royalists, and Neutralists. When U.S. ambassador Unger backed Souvanna Phouma, the latter was restored to office.