Tunisia, cradle of the Arab Spring and widely seen as the country that made the most successful transition from dictatorship to democracy, is now teetering on the brink of internal conflict as the Arab world continues to be engulfed by upheaval and war.

There are concerns as the political upheaval grows, elements of the former regime of Zein Abidine Ben Ali, driven from power in January 2011, retain considerable influence and maintain ties with the labor unions and the internal security forces and could try to stage a comeback.

"The most successful democratic transition after the 2011 Arab uprisings is now under severe pressure," Oxford Analytica warned.

The cause of Tunisia's slide toward anarchy was the assassination Thursday of secular opposition leader Mohammed Brahmi, a member of the 217-seat parliament who represented the central city of Sidi Bouzid, his hometown.

That's where the January 2011 uprising that toppled longtime dictator Zine al-Abidine Ben Ali began when a humble fruit seller committed self-immolation to protest the tyranny of the regime.

Brahmi, 58, one of the top figures in the Arab People's Party, was shot 14 times by a gunman on a motorcycle outside his home in Cite el-Ghazala, a Tunis suburb, in full view of his wife and handicapped daughter.

That was the second killing of an opposition political leader this year. Chokri Belaid of the leftist Popular Front was gunned down in the capital in broad daylight Feb. 6.

Both men were outspoken critics of the Ennahda party of moderate Islamists that has dominated Tunisia since elections in October 2011, and their extremist rivals.

No one has yet claimed responsibility for Brahmi's killing. His wife blamed Ennahda but Tunisian security authorities said the two near-identical shootings were both carried out by the same jihadist assassin.

Interior Minister Lotfi Ben Jeddou identified the suspect as Paris-born Tunisian Abu Bakr el-Hakim, a hardline jihadist and veteran of the Iraq war who's been linked to the Ansar al-Sharia organization, the most radical Salafist group in Tunisia.

Ben Jeddou said one gun, a 9mm semi-automatic weapon, was used in both killings by men riding motorcycles.

Ansar al-Sharia, headed by veteran Salafist Seifallah ben Hassine, has been designated a terrorist organization affiliated to al-Qaida by the U.S. government and the United Nations.

The group has been blamed for the Sept. 14, 2012, ransacking of the U.S. Embassy in Tunis.

In May, security officials linked Ansar al-Sharia with terrorists operating along the border with Algeria, where Tunisian soldiers have been killed recently in shootouts with gunrunners.

Belaid's killing triggered a political crisis that eventually brought down the cabinet of Prime Minister Hamadi Jebali of Ennadha that has ruled Tunisia with two center-left parties since elections that followed Ben Ali's downfall.

Jebali was replaced by Ali Larayedh, the interior minister, who ordered a roundup of terrorist cells he said was affiliated with al-Qaida in the Islamic Maghreb, the main jihadist network operating across northern and northwestern Africa.

The Brahmi slaying intensified the unrest, sparking massive anti-government demonstrations with calls for the resignation of the elected assembly and the governing coalition who have been blamed for failing to curb growing extremism.

At least 65 opposition lawmakers have quit parliament and one cabinet minister has resigned.

"Protests will continue," Oxford Analytica said, "but for now the opposition lacks the popular support needed to engineer an Egyptian-style ousting of the Islamist-led government. The Tunisian military, historically apolitical, is staying on the sidelines.

"Although Ennahda refuses to relinquish power won at the ballot box, it will offer concessions in the hope of resolving the crisis. It may also compromise on the constitution to accelerate the transition to elections, promised by year-end or early 2014."

Opposition parties are calling for a government of "national salvation." But this has not yet gathered sufficient momentum to threaten Larayedh's government.

The big danger is that hardline Islamists are growing increasingly bolder, with Belaid and Brahmi apparently targeted for their criticism of them.

Ennahda, once ambiguous toward the hardline Islamists, has in the last three months taken a tougher line. But it has little to show for it.

Meantime, some 2,000 young Tunisians, possibly more, reportedly have gone to Syria to join rebels fighting the Damascus regime and could return to wage jihad in their homeland.