The strike came a day after hundreds of pro-Maoist demonstrators set fire to vehicles and vandalised shops in western Nepal, in response to the deaths of the illegal settlers in Kailali district on Friday.
Nepal's Human Rights Commission called on the government to investigate the clashes that broke out when police tried to remove thousands of squatters from a forest in Lamahi, about 640km west of Kathmandu.
The Maoists quit the government in May after Ram Baran Yadav, the president, overrode their attempt to sack General Rookmangud Katawal, the head of the army.
Led by Prachanda, the former prime minister, the Maoists have said that the president's decision undermined the civilian government and have since staged regular protests.
Randy Berry, the US charges d'affairs in Nepal, met Madhav Kumar Nepal, the prime minister, on Friday to express "deep concern" about the political deadlock, a US embassy statement said.
Berry told Nepal that Washington is concerned that the Maoists' actions are inconsistent with their stated commitment to the peace process, the rule of law, and democratic practices, the statement said.
The Maoists gave up armed revolt in 2006 but have since been accused of stoking violence and organising protests against the new government.