Salem Labyedh, Tunisia's education minister, has resigned, according to the prime minister's spokesman, as pressure mounts on the Islamist-led government to step down.
Labyedh's resignation on Wednesday came amid growing protests against the ruling Ennahda party, which has been blamed for the killing of an opposition member of parliament last week, the second to be shot dead in six months.
Opposition parties, the largest labour union and the secular Ettakatol party, Ennahda's junior coalition partner, have all called for the government to cede power.
Labyedh, a secular independent, had said he was considering resigning after Mohamed Brahmi, a fellow leftist politician, was killed on Thursday.
The government has blamed Salafists for the assassination, but the opposition accuses Ennahda of being responsible for his death.
While politicians feud, the army is struggling to contain armed fighters, who killed eight soldiers on Monday in a mountainous region near the Algerian border in one of the largest attacks on Tunisian troops in decades.
A small roadside bomb exploded on Wednesday south of Tunis as a police patrol passed, but no injuries or damage were reported.
Last Saturday, the day of Brahmi's funeral, Tunis was hit by its first car bomb, but again no one was hurt.
"We are facing two choices. Either we confront terrorism together, or we will distract the army and security forces with political battles that are much less dangerous than terrorism," Noureddine Bhiri, spokesman for Prime Minister Ali Larayedh, said.
Ennahda has softened its rejection of opposition demands in the face of increasing pressure.
It said on Tuesday it was open to the possibility of a new government, but has firmly rejected the opposition's demand that the transitional Constituent Assembly also be disbanded.
The body is just weeks away from completing a draft of a new constitution to be put to a popular referendum.
Larayedh will meet the head of the powerful Tunisian General Labor Union on Thursday to discuss the political crisis and a new initiative to deal with the situation, his office said.
The 600,000-strong union is calling for a compromise that would remove the current government and put a technocratic government in place, but would not dissolve the Assembly.