Liberia's President Ellen Johnson-Sirleaf on Saturday called on voters to ignore a poll boycott ordered by her rival, saying the move was illegal and intended to intimidate Liberians.
Winston Tubman, the challenger in a presidential run-off vote due on November 8, on Friday said he would not take part in or recognise the results of the poll as the process was biased against him.
The boycott risks derailing Liberia's second post-war election, viewed as a measure of how far the minerals-rich nation has come since years of war ended in 2003.
The election commission has vowed voting will take place anyway but Tubman has called for his supporters to take part in a protest due later on Saturday.
"Do not succumb to fear and intimidation. Do not allow any politician to hold our country hostage," Johnson-Sirleaf said in a radio address to the nation.
"Do not allow Mr Tubman to falsely claim boycott when what he is doing is forfeiting the rights of the finals because he fears defeat," she added.
Newly named Nobel peace laureate Johnson-Sirfleaf led after the first round with 43.9 percent of the vote and has since secured the support of third-placed former rebel leader Prince Johnson, who secured 11.6 percent.
Tubman, a former United Nations diplomat who took 32.7 percent in the first round, has sought to have the election commission revamped in-between the rounds.
The election commission chief resigned as a result but Tubman said the changes were not enough and on Friday said he would "never grant legitimacy to a corrupt political process".
In a sign of mounting concerns over the situation, the U.N., which still has a 9,000-strong peacekeeping force in the country, issued a statement after the boycott call on Friday calling on Liberians to refrain from violence.
West Africa's regional body ECOWAS has been trying to convince Tubman to stand in the run-off and was due to issue a statement later on Saturday.
Johnson-Sirleaf has been credited with restoring stability and starting development after 14 years of conflict but critics argue that progress has been too slow and issues like rampant corruption and poor basic services have not been addressed.
While many Liberians are tired of years of unrest, analysts say Tubman and running mate George Weah, a former football star who is popular with the youth, may seek to tap into simmering frustrations.
Billions of dollars in mining and oil deals have been signed since Johnson-Sirleaf came to power after elections in 2005 and a successful poll would likely intensify investment interest in the West African nation.