TUNIS, Tunisia — Angry anti-government demonstrations broke out Thursday across Tunisia after gunmen killed the leader of a leftist opposition party, raising fears of new chaos on the difficult road to democracy in the cradle of the Arab Spring.

Just five months after a similar assassination plunged the country into crisis, two gunmen shot Mohammed Brahmi, leader of the Popular Current party, in his car outside his home.

Tunisia is struggling after overthrowing dictator Zine El Abidine Ben Ali in January 2011. Many Tunisians are fed up with the government led by the moderate Islamist ruling party, Ennahda, which appears unable to handle a faltering economy, address popular unrest over unmet expectations and crack down on a rising extremist Islamist movement.

Protesters immediately blamed the latest killing on the government. Soon after news broke, crowds gathered outside the Interior Ministry in the heart of Tunis calling for its downfall.

There were also demonstrations around the country, including in Sidi Bouzid, Brahmi's impoverished home town and the birthplace of the country's revolution. Crowds in the nearby town of Meknassi burned down the local headquarters of Ennahda, which rules in a coalition with two secular parties.

The Popular Front coalition of leftist parties that included Brahmi's called for "civil disobedience in all locations of the country until the fall of the governing coalition."

The country's largest trade unions called for a general strike Friday that will shutter the government, public transportation and most shops freeing people up for what are expected to be large anti-government protests.

There were no immediate claims of responsibility for Brahmi's killing. The two attackers sped off on a moped, according to a neighbor cited by the state news agency. Local media reported Brahmi was shot 11 times and his daughter witnessed his killing.

The killing immediately brought to mind the assassination of Chokri Belaid, also a member of the Popular Front coalition, who was killed in his car outside his home in February.

Many members of Belaid's party hold the government responsible for his assassination, believing it either turned a blind eye to Islamist extremists or actively used them to target their opponents. The government has blamed Belaid's assassination on Islamist militants and said that six suspects are still on the run and their names will soon be revealed.

Belaid's death prompted nationwide demonstrations and the resignation of the prime minister. The latest killing is threatening to plunge Tunisia back into the same kind of crisis.

"This day signifies the death of the democratic process in Tunisia," Nejib Chebbi of the liberal opposition Jomhouri (Republican) Party told local radio. "The government must leave."

Crowds gathered outside the hospital in a suburb of Tunis where Brahmi's body was laid out after he was shot. They then swarmed the ambulance taking it away for the official autopsy.

The Ennahda Party, which dominated legislative elections in October 2011, could be severely weakened by the latest assassination, experts said.

"This is really going to put Ennahda on the spot right now," said Laryssa Chomiak, director of the Tunis-based Institute for Maghreb Studies. "The Tunisian public was not happy with the way in which the Chokri Belaid assassination investigation was dealt with... if they mess this up, I think it's going to be extremely bad for them, for their domestic support."

The leader of Ennahda, Rachid Ghannouchi, told The Associated Press he was "very shocked" by the latest assassination, which comes just as the country needs stability to complete the new constitution and political transition.

"Tunisia was getting ready to crown its efforts to complete its transition, it was the last candle still lit," he said, referring to other Arab countries that revolted against dictatorship, but have since known political instability. "The enemies of democracy want to snuff it out to enmesh Tunisia in the troubles found in the other countries of the Arab Spring."

On July 3, Egypt's elected Islamist government was overthrown by a military coup – an event closely watched by other Islamist parties that came to power in post-Arab Spring elections.

The killing comes as Tunisia was celebrating the 56th anniversary of becoming a republic after gaining independence from France. Mustapha Ben Jaafar, the speaker of the national assembly in which Brahmi was a legislator, announced Friday would be a day of mourning.

The new assassination comes as Tunisia's drawn-out transition approaches a milestone. The new constitution has been written and will be voted on in the coming weeks. Prime Minister Ali Larayedh promised on Monday that elections for a new president would be held before the end of the year.

The U.S. State Department, the United Nations and Amnesty International called for an impartial investigation into the killings and for Tunisians to avoid reacting with violence.

"I urge all actors in Tunisia – government, opposition, the general public and civil society – to stand firm and united in the face of political violence, and defend everyone's freedom to hold and express diverse political views," U.N. High Commissioner for Human Rights Navi Pillay said.

U.N. Secretary-General Ban Ki-moon said, "This heinous act must not be allowed to derail the progress that Tunisia continues to make in its democratic transition, including on the constitution, and in meeting the social and economic aspirations of the Tunisian people."

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Associated Press writer Peter Spielmann at the United Nations contributed. Schemm reported from Rabat, Morocco.

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  • A Tunisian supporter of the Popular Front party reacts at Mahmoud Materi hospital, after Mohammed Brahmi died from his wounds after he was shot to death in his car outside his home, north of Tunis, Tunisia, Thursday, July 25, 2013. (AP Photo/Amine Landoulsi)

  • Tunisians take part in an anti-government demonstration outside the Interior ministry on July 26, 2013 in Tunis after the killing of the opposition politician Mohamed Brahmi. (FETHI BELAID/AFP/Getty Images)

  • Tunisians take part in an anti-government demonstration on the Habib Bourguiba Avenue on July 26, 2013 in Tunis after the killing of the opposition politician Mohamed Brahmi. (FETHI BELAID/AFP/Getty Images)

  • The widow of murdered opposition figure Chokri Belaid, Basma Khalfaoui (C) takes part in an anti-government demonstration on the Habib Bourguiba Avenue on July 26, 2013 in Tunis after the killing of the opposition politician Mohamed Brahmi. (FETHI BELAID/AFP/Getty Images)

  • Demonstrators try to remove barbed wire that blocks the access to the Interior ministry on July 26, 2013 in Tunis after the killing of the opposition politician Mohamed Brahmi. (FETHI BELAID/AFP/Getty Images)

  • Tunisian protesters shout slogans during an anti-government demonstration on the Habib Bourguiba Avenue on July 26, 2013 in Tunis after the killing of the opposition politician Mohamed Brahmi. (FETHI BELAID/AFP/Getty Images)

  • A Tunisian protester raises up a national flag near security forces during an anti-government demonstration on the Habib Bourguiba Avenue on July 26, 2013 in Tunis after the killing of the opposition politician Mohamed Brahmi. (FETHI BELAID/AFP/Getty Images)

  • Mubarka Brahmi (L), the wife of opposition politician Mohamed Brahmi, and his son, mourn at their home in Ariana, outside Tunis, after Brahmi was gunned down in front of his home on July 25, 2013. (FETHI BELAID/AFP/Getty Images)

  • Protesters gather on the main avenue of Tunis after the leader of a leftist Tunisian opposition party, Mohammed Brahmi, was gunned down as he left home, in Tunisia, Thursday, July 25, 2013. (AP Photo/Hassene Dridi)

  • Protesters gather on the main avenue of Tunis after the leader of a leftist Tunisian opposition party, Mohammed Brahmi, was gunned down as he left home, in Tunisia, Thursday, July 25, 2013. (AP Photo/Hassene Dridi)

  • In this photo dated Thursday, July 25, 2013, assassinated Tunisian opposition politician Mohammed Brahmi's daughter, Balkis, holds a Tunisian flag as she mourns his death at Mahmoud Materi hospital, north of Tunis, Tunisia. (AP Photo/Amine Landoulsi)

  • Tunisians shout slogans in front of the Interior Ministry after the killing of opposition politician Mohamed Brahmi early on July 26, 2013 in Ariana, outside Tunis. (FETHI BELAID/AFP/Getty Images)

  • A Tunisian supporter of the Popular Front party reacts at Mahmoud Materi hospital, after Mohammed Brahmi died from his wounds after he was shot to death in his car outside his home, north of Tunis, Tunisia, Thursday, July 25, 2013. (AP Photo/Amine Landoulsi)

  • A Tunisian supporter of the Popular Front party reacts at Mahmoud Materi hospital, after Mohammed Brahmi died from his wounds after he was shot to death in his car outside his home, north of Tunis, Tunisia, Thursday, July 25, 2013. (AP Photo/Amine Landoulsi)

  • A Tunisian plainclothes police officer secures the house of Mohammed Brahmi after he was shot to death outside his home in Tunis, Tunisia, Thursday, July 25, 2013. (AP Photo/Amine Landoulsi)

  • TUNISIA-POLITICS-ASSASSINATION

    Mubarka Brahmi (C-L), the wife of opposition politician Mohamed Brahmi, receives condolences from Tunisians at her house in Ariana, outside Tunis, after Brahmi was gunned down in front of his home on July 25, 2013. Tunisia marked a day of mourning after gunmen killed Brahmi, sparking fresh political turmoil, protests and a general strike which took Tunis to near standstill. AFP PHOTO / FETHI BELAID (Photo credit should read FETHI BELAID/AFP/Getty Images)

  • Tunisian lawyer Leila Ben Debba (C) reacts outside a hospital after the killing of opposition politician Mohamed Brahmi on July 25, 2013 in Ariana, outside Tunis. (FETHI BELAID/AFP/Getty Images)

  • Tunisians react in a hospital after the killing of the opposition politician Mohamed Brahmi on July 25, 2013 in Ariana, outside Tunis. (FETHI BELAID/AFP/Getty Images)

  • Belkaeis Brahimi, the daughter of Tunisian opposition politician Mohamed Brahmi, shouts slogans outside a hospital after her father was killed on July 25, 2013 in Ariana, outside Tunis. (FETHI BELAID/AFP/Getty Images)

  • Tunisians react outside a hospital after the killing of the opposition politician Mohamed Brahmi on July 25, 2013 in Ariana, outside Tunis. (FETHI BELAID/AFP/Getty Images)

  • Tunisian police officers inspect Mohammed Brahmi's car in which he was shot to death outside his home in Tunis, Tunisia, Thursday, July 25, 2013. (AP Photo/Amine Landoulsi)

  • Supporters of the Popular Front party gather at Mahmoud Materi hospital, north of Tunis, in support of Mohammed Brahmi who was shot to death in his car outside his home, in Tunisia, Thursday, July 25, 2013. (AP Photo/Amine Landoulsi)

  • Tunisians react outside the hospital in Ariana, outside Tunis, after the killing of the opposition politician Mohamed Brahmi on July 25, 2013. (FETHI BELAID/AFP/Getty Images)

  • Mubarka Brahmi (R), the wife of opposition politician Mohamed Brahmi, cries at the hospital in Ariana, outside Tunis, after her husband was gunned down in front of his home, near the capital, on July 25, 2013. (FETHI BELAID/AFP/Getty Images)

  • Belkaeis Brahmi, the daughter of Tunisian opposition politician Mohamed Brahmi, covers her face with a national flag as she reacts outside a hospital after her father was killed on July 25, 2013 in Ariana, outside Tunis. (FETHI BELAID/AFP/Getty Images)