Somalia's prime minister has refused to comply with an order from the president for him to leave office.
Omar Abdirashid Ali Sharmarke said President Sheikh Sharif Sheikh Ahmed did not have the power to dismiss him and vowed to remain in office.
The BBC's Peter Greste says the row has effectively crippled the government and driven it to the verge of collapse.
It comes at time when the UN-backed government is battling an insurgency against Islamist extremists.
Our correspondent says the administration of President Ahmed has failed to bring either unity or security as he promised when he took charge at the start of 2009.
On Sunday the speaker told journalists that MPs had passed a vote of no confidence in the government.
This was disputed and MPs later voted to remove speaker Sheikh Aden Madobe, who has agreed to step aside.
As this was happening, Islamist rebels fired mortars at the parliament building in the capital, Mogadishu. It was the first time the MPs had met there this year.
Mr Sharmarke, a former diplomat, is the son of a former president who was killed in 1969 ahead of the military coup that brought Siad Barre to power.
Somalia has not had a functioning central government since he was ousted in 1991.
The government rules only a few strategic square kilometres of the capital.
A 5,000-strong African Union peacekeeping force is all that stands between it and the insurgents who now dominate most of the rest of southern and central Somalia.
Some analysts believe the crisis could trigger the government's complete collapse and hand the country to the Islamist rebels.
That depends as much on what the AU decides to do with its troops, as it does on whether the government can overcome its current divisions, our correspondent says.