Forces loyal to unpopular Yemeni President Ali Abdullah Saleh have attacked anti-government protest camps south of Sana'a, killing three and injuring over two dozens of people.

"Large groups from the ruling party attacked the protest headquarters with stones and batons, and 25 people were injured including six in critical condition," a protest leader in the town of Ibb, south of the capital, was quoted by Reuters as saying on Sunday.

Meanwhile, opposition forces have called on protesters to continue their anti-government drive.

Mohammed Sabri, a leading member of the Common Forum opposition collation said "the president is a political corpse," AFP reported.

He said the dysfunctional character of his leadership was proven by the ruler's recent refusal to accept a proposal by the opposition and religious figures to give in to a "peaceful transition of power."

Saleh has already been in office for 33 years with several opposition members arguing that his long-promised reforms have not materialized. He has repeatedly said that he would stay in power until the end of his term in 2013.

The protests began to sweep the country in January. Dozens of people have been killed and hundreds more have been injured in crackdowns by security forces.

"We have called upon the people to widen demonstrations, and escalate the peaceful struggle in all regions until he (Saleh) is left with one option, that is to leave," Sabri said.