Fighters used mounds of earth to barricade roads, while armed men and vehicles mounted with machine guns were stationed in opposition strongholds after the fighting that left three dead.
“Both the Somali security forces and the pro-opposition fighters have taken positions along some key roads,” witness Abdullahi Mire told AFP.
The fragile nation has not had an effective central government since the collapse of a military regime in 1991 led to decades of civil war and lawlessness fuelled by clan conflicts.
For more than a decade, conflict has centred on an Islamist insurgency by the Al-Qaeda-linked Al-Shabaab.
The political clashes in the streets of Mogadishu mark a dangerous new phase in a dispute triggered by the failure to hold February’s planned elections.
President Mohamed Abdullahi Mohamed, best known by his nickname Farmajo, earlier this month signed a law approved by parliament that extended his mandate by two years.
On Sunday night, sporadic bursts of heavy gunfire rang out across the capital after fighting broke out between government forces and soldiers allied along clan lines to various opposition leaders.
Three people — two police officers and one opposition fighter — were killed in the clashes, police said Monday.
Tensions remained high, with soldiers supporting the opposition vowing to remove the president by force.
“Former president Farmajo is a dictator… he wants to stay in power with force. We are against that, we will continue fighting until he leaves,” said military commander Abdulkadkir Mohamed Warsame, who backs former Prime Minister Hassan Ali Khaire and was running against Farmajo for the presidency.
“Now we want to take over the presidency,” said Warsame, adding the opposition controlled the northern Hawle Wadag district.
“We will not stop our fighting — we can stop only when we die.”
The fighting had “sharpened” clan divisions in the capital and set the stage for more violence along those lines, said Somalia analyst Omar Mahmood.
“Any sort of miscalculation could happen… it just takes one trigger-happy soldier to fire on the other side, and that’s going to erupt those dynamics,” the senior analyst for the International Crisis Group told AFP.
Some residents in tense neighbourhoods had begun leaving their homes.
Former president Hassan Sheik Mohamud said Sunday that “forces loyal to” Farmajo had attacked his house. The government denied this, saying security forces had foiled attacks by an “organised militia”.
While schools and universities were closed, life in some of the unaffected neighbourhoods proceeded much as usual.
Prime Minister Mohamed Hussein Roble expressed disappointment Monday with the violence during Ramadan, and urged security forces to “fulfil their national commitment and protect” Mogadishu’s people.
Farmajo’s four-year mandate expired in February before fresh elections could be held, leading to a constitutional crisis and to opposition leaders refusing to recognise him.
The crisis mushroomed from a long-simmering disagreement between Farmajo and the leaders of Puntland and Jubaland, two of Somalia’s five semi-autonomous states, over how to conduct elections.
Multiple rounds of UN-backed talks failed to find a solution, and parliament pushed through the bill extending his mandate for two years.
The crisis has dismayed Somalia’s foreign backers, who have urged Farmajo to resume dialogue with the federal states.
“The problem is, every time you have an outbreak of violence like this, it just further widens the gulf between the parties and really makes getting to any sort of agreement that much harder,” said Mahmood, the ICG analyst.
The British embassy and European Union envoy in Mogadishu expressed alarm over the violence, while the UN Mission in Somalia tweeted that “violence is not the solution”.
UN Secretary-General Antonio Guterres added he was “deeply concerned” about the clashes, urging “all Somali stakeholders to resume negotiations immediately”.
The US State Department also expressed worry, adding that they were “prepared to consider all available tools, including sanctions and visa restrictions,” to tackle the instability.