confirmed their ability to distribute weapons and even assassinate key Iranian leaders of the coup. Hence, with a disciplined party membership, backed by military officers with access to weapons, the Tudeh had a strong hand." With the TPMO decimated, the Tudeh network was compromised as the TPMO had "acted as a shield for the party" and helped preserve it immediately after Mosaddeq's overthrow. "Many high- and middle-ranking Tudeh leaders were arrested or forced to flee the country. The arrest and execution of Khosro Roozbeh in 1957-8 signaled the end of this process." Tudeh verdict After the fact, the party engaged in self-criticism of its policies toward Mosaddeq at its Fourth Plenum held in Moscow in July 1957. They found them "sectarian and leftist" and did not to recognizing "the progressive nature" of the oil nationalization movement. Late 1950s and 1960s The Sino–Soviet split caused some splintering of the party in the early 1960s, with at least one Maoist group breaking away. In the mid-1960s, the U.S. State Department estimated the party membership to be approximately 1500. In 1965, the party faced a second division between the mainstream of the organization and the splinter faction, which advocated a violent struggle against the government by arming the tribes of southern Iran. This faction caused a great deal of damage and three years passed before the unity of the party was restored. The remnants of this faction are known as the Labour Party of Iran. In 1966, several party members, including Ali Khavari and Parviz Hekmatjoo of the Central Committee, and Asef Razmdideh and Saber Mohammadzadeh, were arrested and sentenced to death. This sparked an international outcry and hunger strikes in Europe which forced the government to reduce the sentences to life imprisonment. These events created much international sympathy for the worker's struggle in Iran and helped unify the party after the split. The Tudeh Party from this point on becomes established as one of the strongest underground movements and helps to pave the way for the forthcoming Iranian Revolution of 1979. Iranian Revolution of 1979 In the early 1970s, the Iranian guerrilla movement began in northern Iran in the province of Mazandaran. The 1970s also witnessed the birth of widespread worker strikes and demonstrations, and university campuses became a hotbed of revolutionary activity. In 1973, Tudeh released a brochure titled "Oil from Iran and imperialist oil monopolies," likely advocating for oil nationalization.