In December 1956, several army commanders in Sumatra announced they had taken over civil government. This crisis spread and in March 1957, the military commander of East Indonesia imposed martial law over his command area. On March 1957 the cabinet resigned and Sukarno proclaimed martial law nationwide. In May 1957, PSI economist Professor Sumitro Djojohadikusumo left Jakarta for Sumatra, followed by other political figures. In January 1958, the PSI demanded a new cabinet, and the following month dissidents in Padang, West Sumatra issued an ultimatum demanding the dissolution of the cabinet within five days. Despite efforts by the PSI in Jakarta to forestall a rebellion, on 15 February a rebel government was proclaimed in Bukitinggi called the Revolutionary Government of the Republic of Indonesia (PRRI). It was headed by Amir Sjarifoeddin as Prime Minister and included Burhanuddin Harahap from the Masyumi Party and Sumitro Djojohadikusumo. Hatta and PSI leaders in Jakarta called for a negotiated settlement, but the government decided on a military solution, which defeated the rebellion by mid-1958.