The leftist party led by El Salvador's president lost four seats in midterm elections, leaving the conservatives as the biggest bloc in the legislature, according to preliminary vote counts made public Monday.
The Supreme Electoral Tribunal said that with 95 percent of Sunday's votes counted, the right-wing Nationalist Republican Alliance gained a seat to hold 33 of the Legislative Assembly's 84 seats. It also won some key mayorships, including in the capital.
President Mauricio Funes' Farabundo Marti National Liberation Front dropped to 31 seats from 35. A coalition led by former conservative President Elias Saca won 11 seats, while the remaining nine seats went to four small parties.
Funes is the first leftist to be elected El Salvador's president since its civil war ended in 1992.
Observers said the results of Sunday's vote was a setback for Funes, who won the presidency in 2009 leading the ticket of former guerrillas of the Farabundo Marti National Liberation Front.
"They have to carry out a thorough internal analysis, because they lost their hard-core of support. Or the middle class, which has been most affected by the economic changes, may have voted their displeasure," said Rene Portillo, a political expert at the country's Technological University.
A combination of new taxes and increases in the cost of living may have taken a toll on the administration, he said.
Roberto Rubio, an analyst for the non-governmental National Foundation for Development, said, "The FMLN has to reflect and look at its errors."
"If they don't do that, things could go badly for them in 2014," Rubio added.