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. read more
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.