Probes into the assassinations last year of two opposition figures that plunged Tunisia into crisis have gathered pace this week, with authorities saying they arrested a suspect and killed another in a firefight.

Early on Sunday, the interior ministry said it arrested a man suspected of involvement in the murder of leftist MP Mohammed Brahmi after a fierce gun battle during an overnight raid on a militant hideout near Tunis.

Tunisian security forces arrested a suspect in the murder of opposition politician Mohamed Brahmi after a fierce gunbattle during an overnight raid on a militant hideout, the interior ministry's spokesman said Sunday.

Brahimi was the second of two opposition politicians to have been assassinated last year by suspected jihadists as Islamist violence rocked the North African country, which was the birthplace of the Arab Spring revolutions in 2011.

U.S. diplomats on Friday walked out of the ceremony to celebrate Tunisia's new constitution after Iran's representative made "false accusations" about Washington undermining the Arab Spring uprisings, the embassy said.

In his address to the National Constituent Assembly (NCA), Iran's parliamentary speaker Ali Larijani accused arch foes the United States and Israel of seeking to thwart the pro-democracy uprisings that swept the region in 2011.

French President Francois Hollande on Friday promised President Michel Suleiman to start equipping the Lebanese Army with weapons “as soon as possible.”

Hollande also reiterated “Paris' commitment to supporting Lebanon” during a meeting with Suleiman in Tunisia, where they took part alongside world leaders in a ceremony celebrating the adoption of the country's new constitution.

President Michel Suleiman participated on Friday in a ceremony in Tunisia to celebrate the adoption of the country's new constitution three years after the revolution and attended by the heads of state.

Suleiman voiced hope during a brief speech before the Tunisian national assembly that Tunis enjoys stability and prosperity after the adoption of the new constitution.

Tunisia celebrated Friday the adoption of a new constitution three years after the revolution, a landmark in getting its troubled transition back on track and hailed as a model by foreign leaders.

A ceremony at the national assembly, where the constitution was adopted on January 26, burnished Tunisia's positive image in contrast with other Arab Spring nations, such as Libya and Egypt, which remain plagued by instability and political turmoil.

The International Support Group for Lebanon is expected to meet in March in Paris at the invitation of France for the establishment of two funds the first to support Lebanon's economy and the second to aid the Syrian refugees in the country.

Sources told An Nahar newspaper that the meeting will seek to set a plan to grant Lebanon the funds to offer it financial support amid the acute crisis it's suffering from due to the ongoing conflict in Syria.

Tunisians on Thursday marked 12 turbulent months since the assassination of opposition politician Chokri Belaid, with his family still demanding to know what happened despite the alleged assassin being shot dead this week.

The charismatic leftist and virulent critic of the Islamist party Ennahda, then in power, was gunned down outside his Tunis home on February 6, 2013.

A Tunisian-born scientist accused of plotting to derail a passenger train in Canada said in a newspaper interview published Wednesday his aim was to protest the U.S.-led military mission in Afghanistan.

"My aim is very simple: to give them a message," Chiheb Esseghaier told the daily National Post.

The family of slain Tunisian opposition politician Chokri Belaid renewed their demand Wednesday for the truth about his assassination, after the alleged perpetrator was killed in an anti-terrorist operation.

The interior ministry said Kamel Gadhgadhi, accused of shooting Belaid dead at close range on February 6, 2013, was among seven militants killed in a 20-hour operation launched on a house in a Tunis suburb on Monday.