Youths complain that promises have been broken
Tanks have been deployed in parts of southern Yemen after rioting by youths, officials and witnesses say.
Demonstrators blocked a road and burned tyres, and dozens of people, including lawmakers, were arrested, reports say.
The youths complain that promises to give them places in the army have not been fulfilled.
The city of al-Dalea is reported to have been worst hit by the violence, with riot police firing into the air and tanks used to barricade streets.
Witnesses said the security crackdown had left many towns deserted.
Protesters responded to the deployment of security forces by using armed men briefly to cut the main road between the capital, Sanaa, and the port of Aden.
The latest rioting follows three days of disturbances in the south. Around 20,000 people are reported to have demonstrated last week in al-Dalea.
An official quoted by AP news agency said rioters set fire to two police stations in the town on Sunday. Military vehicles were burned and an attempt was made to storm a bank.
Correspondents say the violence stems from long-standing disaffection in the south following the civil war of 1994, which the south lost to the north.
Southerners say a government amnesty granting former southern soldiers re-admission to the army has not been fulfilled.
More generally, southerners feel they are kept out of government jobs which are given to northerners, say correspondents.