In a defiant speech, Tunisia’s prime minister rejected opposition demands that his government step down and promised on Monday to complete the country’s democratic transition with a new constitution by August and elections in December.

The assassination of two opposition legislators in the past six months has plunged Tunisia — the birthplace of the Arab Spring — into a crisis with anti-government protests, the resignation of a cabinet minister and a walkout by dozens of lawmakers.

The standoff was given extra urgency by a bloody ambush Monday that left at least eight soldiers dead in a mountainous region near the Algerian border that is known as an Islamist militant stronghold. Jebel Chaambi, Tunisia’s highest mountain at 5,000 feet, was the site of an intensive military hunt for an al-Qaeda-linked militant group during the spring.

Prime Minister Ali Larayedh’s fiery speech, in which he called those wanting to dissolve the government “anarchists” and “opportunists,” is unlikely to appease an angry opposition that says the Islamist-led government has failed to carry out the political transition promised after the overthrow of Tunisia’s dictator in January 2011.

On Thursday, left-wing Tunisian politician Mohammed Brahmi was assassinated in Tunis, shot 14 times outside his home in front of his family. That followed the killing of another left-wing opposition legislator, Chokri Belaid, in February.

On Sunday night, thousands of people demonstrated in front of the elected assembly charged with writing the country’s new constitution and demanded that it be dissolved along with the government. Dozens of opposition lawmakers have suspended their participation in the assembly, and Education Minister Salem Labiadh submitted his resignation Monday.

Even more serious for the government, the governing coalition appears to be breaking apart. Mohammed Bennour, spokesman for the left-of-center Ettakatol party, said his group wants to withdraw from the coalition and dissolve the government. That would leave the moderate Islamist Ennahda party that dominates the coalition even more isolated.

In his televised speech, Larayedh presented a road map for completing the democratic transition with a new constitution by the end of August and the passage of the needed election laws by Oct. 23 — the anniversary of the date in 2011 that brought the Ennahda party to power.

He said an election for a new legislative body would be held on Dec. 17, the third anniversary of the self-immolation of itinerant fruit seller Mohammed Bouazizi that sparked the uprising that overthrow dictator Zine el-Abidine Ben Ali a month later.