Sana'a - At least seven people were injured, two of them critically, when a hand grenade exploded while police were dispersing protestors in south Yemen on Monday, security sources said.

The assailant threw the grenade while police were trying to break up a peaceful protest against rising prices in the southern province of Dhali, according to the sources.

A policeman was among the wounded, the sources said, adding that the assailant was arrested.

In the port city of Aden police rounded up scores of political activists and journalists ahead of a protest to mark the first anniversary of demonstrations in demand of more rights for the south.

South Yemen had been an independent state with a Marxist regime until 1990 when it united with northern Yemen. An attempt to restore the south's independence was crushed in 1994 following a civil war.

Groups representing people who had retired from army and government jobs in southern Yemen have staged a series of protests in past 12 months in demand of more rights and better services. (dpa)