Tunisian politicians are trying to form a unity government and restore order amid the violence following the toppling of Zine El Abidine Ben Ali, the deposed president.
Soldiers were guarding public buildings after drive-by shootings and prison riots on Saturday in which scores of inmates were killed in the chaos.
There were reports on Sunday of shots being fired near the headquarters of Tunisia's opposition Progressive Democratic Party (PDP) opposition in the centre of the capital, Tunis.
In a statement, the party said that police and military stopped a car carrying of armed men, who it described as foreigners, after which shots were fired.
Al Jazeera's James Bays, reporting from Tunis, said there were few details of the shooting but that there had been other such incidents in the city.
Bays said that even though there are army road blocks set up throughout the city, people are saying that they need to arm themselves against the police, who they do not trust.
"In between the road blocks, we were coming across large groups of people who had their own home-made weapons, axes and steel bars, and some of them were not particularly friendly to us when we wanted to film in the area," he said.
Looting and burning
A tense calm appeared to have descended on Tunis, a day after looters emptied shops and torched the main train station and soldiers traded fire with unidentified armed men in front of the interior ministry.
Some rioters appeared on Saturday to be targeting businesses owned by members of Ben Ali's family. In Tunis, a branch of the Zeitouna bank founded by Ben Ali's son-in-law was torched, as were vehicles made by Kia, Fiat and Porsche - brands distributed in Tunisia by members of the ruling family.
Ben Ali, who had been in power since 1987, fled to Saudi Arabia on Friday following mass protests against his government.
Public television station TV7 broadcast phone calls from residents on Tunis's outskirts, describing attacks by knife-wielding assailants.
Amid the turmoil, Tunisians have organised themselves to protect their neighbourhoods, Amine Ghali, a democracy advocate in Tunisia, told Al Jazeera.
"There is a serious security issue, but people are getting organised. They are standing in front of their neighbourhoods, forming neighbourhood committees ... they are trying to be as calm as possible and trying to help the military," he said.
Residents of some Tunis neighbourhoods set up barricades and organised overnight patrols to deter rioters.
"If the interim government doesn't quickly implement measures to reduce the level of unemployment and increase standards of living, we are going to see more of these protests," Ayesha Sabavala, deputy editor of the Economist Intelligence Unit, told Al Jazeera.
Al Jazeera's Bays said the situation in Tunis on Sunday was "pretty volatile" even for ordinary people.
"We were filming the hardships of the ordinary people of the city - a bread queue ... and then members of the crowd turned on us and said 'it was shameful for you to film us in this situation, begging for bread'," he said, adding that the TV crew just managed to escape the large, angry crowd.
He said the army was rounding up those loyal to Ben Ali, including members of the presidential police.
In the most prominent arrest, Tunisia's former interior minister, the man many held responsible for a police crackdown on anti-government protesters, was held in his home town in the north of the country.
Rafik Belhaj, who was the most senior official in charge of the police force, was arrested in Beja on Sunday afternoon.
Belhaj had been dismissed from his position on Wednesday in one of Ben Ali's final efforts to placate public anger with his leadership.
Separately, Tunisian state television announced that General Ali Seryati, the former head of Ben Ali's security service, would appear in court to face charges of threatening national security and provoking armed violence.
In another development, the AFP news agency reported that a member of the president's extended family had died of a knife wound two days earlier.
Imed Trabelsi, a nephew of Ben Ali's wife, died in a military hospital in Tunis, a staff member told the AFP.
He was the first person in the president's extended family reported to have died as a result of the uprising.
Trabelsi was an influential businessman and became more widely known after he was mentioned in a US diplomatic cable released by WikiLeaks that said he was reported to have stolen a yacht belonging to the chairman of the powerful French financial firm, Lazard.
Salim Shayboub, Ben Ali's son-in-law, also reportedly has been arrested.
Dissident to return
Against this backdrop of instability, the exiled head of one of its leading opposition parties announced his intent to return to the country.
Rashid al-Ghannouchi, the leader of the Islamist Nahdha (Renaissance) party, told Al Jazeera on Saturday that he and other leading figures would "return shortly" to Tunisia.
The Nahdha, formed in 1988, never gained legal status under Ben Ali because of a law prohibiting political parties based on religion.
According to human rights groups, its members have long suffered persecution and torture.
Ghannouchi said Nahdha should be recognised and said that it is ready to take part in a coalition government.
Fouad Mebezaa, the speaker of parliament, was sworn in as the country's interim president on Saturday and promised to create a unity government that could include the long-ignored opposition.
It was the second change of power in Tunisia in less than 24 hours.
Earlier, Mohamed Ghannouchi, the prime minister, went on state television to announce that he had taken power in accordance with the constitution, after Ben Ali fled.