A major gun battle has broken out in the Somali capital, Mogadishu, as MPs meet in the central city of Baidoa to consider the future of the government.
A BBC correspondent in Mogadishu says it is some of the heaviest fighting since Islamists were ousted by Ethiopian-backed troops in December.
He says insurgents may be angry at the attention given to the fallout between the president and his prime minister.
President Abdullahi Yusuf wants parliament to sack the prime minister.
Mr Yusuf and Prime Minister Ali Mohammed Ghedi have been lobbying for support among MPs for the past week ahead of the debate in parliament.
Both men ascended to power with the backing of Ethiopia but have fallen out over reports that they favoured rival concerns interested in oil exploration contracts.
Ethiopian troops are on patrol outside Somalia’s parliament in Baidoa, as the parliamentary showdown looms.
The BBC’s Mohammed Olad Hassan in Mogadishu says the insecurity had shifted to Baidoa until the insurgents attacked a police station near the main market of Bakara on Tuesday evening.
He says the attack has taken people by surprise.
A rocket-propelled grenade hit a group of people as they were having tea.
At least 10 people have been wounded and at least five people, including two civilians, have died in the fighting so far, he said.
The insurgents are heavily armed and have managed to push back government troops even after they received reinforcements.
Meanwhile in Baidoa, where the parliament sits, a vote of confidence has yet to be debated.
But analysts say the crisis threatens to leave Somalia with two governments.
President Yusuf and his allies argue that Mr Ghedi’s term has expired according to the federal charter – but the prime minister disputes this.
Despite having international support, diplomats argue that the transitional government has failed to set up institutions to reconstruct the country.
The UN’s special envoy for Somalia, Ahmedou Ould Abdallah, has warned that the move may derail the peace process.
"I have talked to them and asked them to remain together for the sake of the peace building in Somalia but if it is impossible they should part peacefully," Mr Abdallah told the BBC’s Network Africa programme.