RIO DE JANEIRO — Paraguay’s Senate voted on Friday to remove President Fernando Lugo from office, plunging the country into a political crisis. Mr. Lugo said he accepted the results of the hastily arranged vote, despite describing the efforts to remove him as an “express coup d’état.”

“Today it is not Fernando Lugo who is receiving a coup, but Paraguay’s history, its democracy,” said Mr. Lugo, 61, a former Roman Catholic bishop. He was elected in 2008 with unusually high expectations to ease tension over disparity in landholdings, breaking six decades of one-party rule in Paraguay, one of South America’s poorest countries.
Legislators quickly swore in the vice president, Federico Franco, a medical doctor and a former supporter of Mr. Lugo, as Paraguay’s new leader.
Mr. Lugo’s abrupt removal points to a new phase of political instability in Paraguay, a renowned hub for the trafficking of contraband and drugs. The landlocked country has gone through periods of upheaval since the long, repressive dictatorship of Alfredo Stroessner ended in 1989, including the resignation of one president in 1999 and the impeachment of another in 2003.
The Senate vote came after Paraguay’s lower house of Congress voted Thursday to impeach Mr. Lugo over a clash this month between squatters and the police that left 17 dead. The clash led to the resignation of Mr. Lugo’s interior minister and his chief of police.
The Senate gave Mr. Lugo just two hours to defend himself in a public trial; he declined to appear, sending lawyers to request 18 days to prepare his defense. They were rebuffed by the Senate president, Jorge Oviedo, leading to the vote of 39 to 4.
The removal of Mr. Lugo, who had about a year left in his five-year term, and was eligible to run for re-election, put Paraguay’s neighbors on alert. The Union of South American Nations, or Unasur, a political bloc in which Brazil wields broad influence, sent a diplomatic mission to Asunción, Paraguay’s capital.
In a statement reflecting the unease with which the region watched the events unfold, Unasur issued a statement saying that the ouster of Mr. Lugo “did not respect due legal process.”
The rapidity of the removal may have reflected anger over the clash between the police and squatters. But he faced other accusations in Paraguay’s Congress, including a claim that he broke the law by allowing leftist parties to hold a meeting at an army base. In addition, his opponents were incensed that he signed an agreement allowing Unasur to exert pressure on any of its members if an elected leader was overthrown.
Mr. Lugo’s popularity had already been damaged by paternity claims from his time as a bishop. He admitted in 2009 to fathering one child with a former parishioner, and this month he acknowledged that he was the father of another child, a 10-year-old boy, from a different liaison.
Mr. Lugo’s removal presents a test for Brazil’s leadership in South America. Brazil’s president, Dilma Rousseff, signaled Friday that Paraguay could face sanctions, which could potentially include its expulsion from Mercosur, a trade bloc, and other multilateral groups.
The involvement of Brazil in Paraguay politics is a delicate issue because of its deep economic influence there, exemplified by Itaipu, a huge hydroelectric dam that straddles the Paraná River between the countries. There are also hundreds of thousands of Brazilians and their descendants living in Paraguay.
Mr. Franco, Paraguay’s new president, promptly said after he was sworn in that Paraguay needed to redirect its energy policies to promote industrialization, including a review of electricity exports to Brazil and Argentina.
It remains to be seen how much legitimacy Mr. Franco will have in Paraguay. Yenny Villalba, the executive director of Pojuaju, an association of nongovernmental groups, said Mr. Lugo’s removal, while viewed as legal, “is not legitimate.”
“This is a very risky maneuver that has put the entire population in check,” Ms. Villalba said. “They pushed to breaking point the political equilibrium.”
Lis Horta Moriconi contributed reporting.