Gunshots rang out late on Friday in Somalia's capital Mogadishu, witnesses said, when government troops approached the home of the city's former police commander who was sacked for opposing a move by the president to extend his term.

The stand-off reveals splits within Somalia's security services that threaten to see forces turn on each other, creating an opportunity for the al Qaeda linked al Shabaab insurgency to exploit.

"Somalia's long-running political crisis has entered a new, dangerous phase," said the International Crisis Group, a Brussels-based think-tank, in a briefing note on Saturday.

"The opposition is said to be considering forming a parallel government; cracks have deepened in a security apparatus long divided along clan lines, and the president's opponents have vowed to resist extension of his rule."

Somalia, riven by civil war since 1991, is trying to rebuild with international help, but the path to stability has been obstructed by a political crisis caused by a failure to hold elections that were due in February.

On Monday, lawmakers extended President Mohamed Abdullahi Mohamed's four year term by up to two years.

The resolution passed after then Mogadishu police chief Saadaq Omar Hassan announced parliament was suspended, triggering his sacking moments later.

Hassan retreated to his house in the Shirkole area of the city, which is guarded by 100 armed men who have been reinforced by clan fighters, his family and area residents said.

Calm returned after the burst of gunfire, but some Shirkole residents held street demonstrations in support of Hassan, burning tyres and shouting slogans against the president.

"If you are attacked, you have to defend yourself," said Mahad Mohamed Salad, a pro-Hassan lawmaker.

The government denied claims it wanted to attack Hassan.

"We have no interest attacking a civilian area where most inhabitants are children and women," interior security minister Hassan Hunbdubey said in an online address late Friday.

Donors, who have opposed the president's move to extend his term, fear the crisis could abet further attacks by Islamist al Shabaab militants, who have been trying for years to topple the government.

The militants on Friday killed Mohamed Abdi Hayle, the district commissioner for Hamarjajab on the edge of Mogadishu, the state news agency reported.

They also captured the Becaadweyn area of the central state of Galmudug without resistance on Thursday, after the Somali army left the area, residents said.