At least 12 Yemenis have been killed when armed men exchanged fire with police during protests over a rise in fuel prices, witnesses have said.
Troops were sent out onto the streets to help restore order
Clashes broke out in the capital, Sanaa, and several other towns as marchers attacked government buildings and threw stones at police.
Correspondents say the government wants to curb a budget deficit, but delayed the price hike to avoid causing riots.
The government says it will offset the rise by lowering tax and raising wages.
One witness quoted by AFP said there were five fatalities in the town of Damar about 100km (60 miles) south of the capital. Seven special forces troops were reported wounded.
Another five deaths were reported in Dali, 250km south of Sanaa.
Residents in the capital quoted by Associated Press said two people were killed, including a 12-year old, in an exchange of fire between protesters and security forces.
Some protesters blocked a road to the airport with makeshift barricades and shouted slogans against the prime minister, Abdul Qadir Bajammal, AP reports.
Riot police fired into the air to disperse the crowd.
The government says the price rises, in some cases more than doubling the cost of fuel, are in line with the rise in global oil prices.
Opposition parties say it will hit the poor and are calling for a crackdown on official corruption.
The government is currently implementing harsh economic reforms to address the budget deficit, as well as high unemployment and bureaucracy.