The presidential candidate from El Salvador's right-wing opposition Nationalist Republican Alliance (ARENA) party is extending his narrow lead in the race to win February's election, according to a poll released on Monday.

ARENA candidate Norman Quijano has 35.5 percent of voters' support, while former guerilla commander Salvador Sanchez, candidate for the ruling Farabundo Marti Front for National Liberation, is close behind with 31.8 percent, according to the survey by polling firm Mitofsky.

"I wouldn't call it a technical tie, but it's a close race," Roy Campos, president of Mitofsky Consulting, said in a television interview.

Mitofsky in July had Quijano with 33 percent of voters' support and Sanchez with 32 percent.

The Mitofsky poll shows different results to surveys by the Central American Jesuit University, which have consistently put Sanchez ahead. In December, the latter's poll showed Sanchez leading with 38.4 percent of the vote to Quijano's 33.4 percent.

Both polling firms have former El Salvador president Antonio Saca, who is running for a separate right-wing grouping known as Unidad, in third place. Mitofsky's latest poll said he had 16 percent of support.

The survey, taken between January 3-5, has a margin of error of 3.1 percent.

More than 4 million people are expected to vote in the elections on February 2, in which they will pick a president and vice president who will govern the violent, poverty-stricken country for the next five years.

The winning candidate needs more than 50 percent of the vote to avoid a run-off election, which would take place on March 9.