Clashes broke out on Thursday in at least three towns in the south and north, with government forces, backed by army tanks and armoured vehicles, deployed along main roads, witnesses said.
Four protesters were killed and 10 others were wounded in the town of al-Dali, 250km south of the capital, witnesses said.
An exchange of fire occurred during demonstrations in which protesters damaged vehicles and shops in the town of Loder, in the southern province of Abyan, they said. There were no reports of casualties in Loder.
Similar clashes also raged in the northwestern city of Saada.
Aljazeera's correspondent in Sanaa said violence has erupted even in Eden.
The fiercest clashes took place in the Red Sea port town of Houdeida. Three people were killed when protesters attempted to break into state oil facilities.
In the southern Ta'iz area, two people - one a nine-year-old boy - were killed.
Two policemen were killed in the northern province of Saada
while two civilians died in the eastern province of Marib.
The Houdeida clashes appeared to be the fiercest and
witnesses said shots were fired. Unrest broke out again late on Thursday and heavy gunfire was heard, residents said.
Yemeni army and security forces have been heavily deployed in Sanaa and other major towns in the south where similar clashes broke out on Wednesday during demonstrations.
Tanks and armoured vehicles took up positions on main crossroads in the capital and other towns as patrols roamed main streets, witnesses said.
In Sanaa, loudspeakers mounted on police cars called on residents not to take part in "destructive acts and riots" as "the security and stability of the country is the responsibility of all citizens".
The cabinet announced late on Tuesday that it would put into effect new fuel prices, lifting its subsidies on fuel products.
Petrol prices in the impoverished republic nearly doubled from 35 rials (32 cents) per litre to 65 rials. Diesel jumped from 17 rials to 45 rials.