SANAA (Reuters) - Yemeni soldiers traded gunfire with Shi'ite Muslim rebels near a military base at the southern entrance to the capital Sanaa on Tuesday, residents said, hours after soldiers killed at least four Shi'ite protesters outside the cabinet building.
A civilian was killed in the gun battle and both soldiers and rebels suffered several injuries, government sources said.
The fighting now threatens to bring into the capital a rebellion by Shi'ite Houthi tribespeople that until now been confined to the north.
Earlier, some of the Houthi activists who have been staging protests in Sanaa for weeks had tried to force their way into the cabinet building.
Medical sources said four protesters had been killed.
A security source told the state news agency Saba that protesters had shot at security personnel guarding the cabinet building and nearby state radio, but denied that the security forces had fired live bullets back.
Houthi spokesman Mohammed Abdul Salam said the demonstrators had been unarmed, adding: "The authorities want the people to realize that peaceful options aren't acceptable ... and are no use in correcting the situation."
The Houthis said dozens of activists had been wounded.
Protesters have been blocking the main road to Sanaa's airport and holding sit-ins for weeks at ministries in an attempt to oust the government and restore fuel subsidies.
The Houthis accuse the government of the desperately poor southern Arabian country of corruption, while critics say the Houthis are trying to grab power and carve out a semi-independent state for themselves in the north - something they deny.
While activists have been demonstrating in the capital, armed rebels in the northerly al-Jawf province have been fighting government-allied tribes backed by air strikes over the last three days.
Both sides vowed defiance on Monday, as the International Crisis Group think tank said Yemen's political transition was at "a crossroads more dangerous than any since 2011," when mass protests ousted veteran autocrat Ali Abdullah Saleh and security around the country sharply deteriorated.
"The Houthi group may not and cannot continue its escalation and its disturbance of the public tranquillity and the undermining of security and stability in the capital," said Salah's successor, President Abed Rabbo Mansour Hadi.
Houthi leader Abdel Malik al-Houthi said: "We vow to continue in our position and dismiss any questioning of our intentions. The solution is to respond definitively to the popular demands, and we are serious in these demands."
Separately, al Qaeda militants detonated a car bomb at an army checkpoint in the eastern Hadramawt province, setting off a firefight in which three soldiers and 10 militants were killed, a local security source said.
The United States and Yemen's energy-rich Gulf neighbors fear for its stability as it battles al Qaeda in the Arabian Peninsula, one of the fiercest affiliates of the global militant group, and struggles with sectarian rifts that have led to warfare in other Arab countries.
Additional reporting by Mohammed Mukhashaf in Aden, Writing by Noah Browning; Editing by William Maclean and Kevin Liffey