Tanks have been deployed in Yemen's capital Sanaa and other towns as a second day of violent protests claimed the lives of at least six people.
Presidential homes and government buildings are being guarded
Clashes between rioters and security forces on Wednesday killed 13 people.
Demonstrations broke out in Sanaa and towns in the north and south after fuel subsidies were lifted on Tuesday, leading to a dramatic rise in prices.
The government says it needs to reduce the budget deficit, but opponents say the rises hit poor people the hardest.
Three protesters were believed to have been killed trying to storm oil facilities in the Red Sea port city of Hudaydah on Thursday.
Witnesses said they were fired on by anti-riot police trying to protect the facility, Reuters news agency said.
In the northern city of Saada, at least two people were killed, reportedly members of the security forces.
And there were reports that at least one person had been killed in clashes in Sanaa.
The 13 people who died on Wednesday included a 12-year-old child. They were killed as marchers took to the streets, attacking government buildings and throwing stones at the police.
Some blocked a road to the airport with makeshift barricades.
Tanks and armoured vehicles were seen taking up positions on main crossroads in the capital, and in at least three other towns.
They were also guarding the presidential palace and government buildings in Sanaa, according to one report.
Loudspeakers on police cars urged residents to refrain from taking part in "destructive acts and riots", saying security and stability were "the responsibility of all citizens".
Prime Minister Abdul Qadir Bajammal has appealed for calm and called on people to "differentiate between freedom of expression and freedom of destruction".
The government seems alarmed that the protesters have not only damaged cars and shops, but are directing their anger at the president and the ruling party, says the BBC's Roger Hardy.
Yemen is one the poorest countries in the Arab world, and the government is implementing harsh economic reforms to address its heavy debts.
By lifting subsidies on fuel, the government has virtually doubled the price of petrol and significantly increased the price of diesel.
It says the rises will be offset by lower taxes and increased wages.
But opposition parties say the move hits the poor, and are calling for a crackdown on corruption by officials.