At least nine protesters have been killed in the Yemeni capital, Sanaa, after security forces opened fire on a demonstration demanding immediate exit of the president, hospital officials say.
Separately on Wednesday, troops reportedly shot dead three protesters and wounded others in a gunfight in Aden.
Residents in at least 18 cities and towns across the country launched a civil disobedience campaign on Wednesday protesting against a plan which would give Ali Abdullah Saleh a month-long window to resign.
The opposition bloc agreed Tuesday to take part in a transitional government under the Gulf-negotiated deal, which gave Saleh immunity for him and his family.
The balance of power has tipped against Saleh, who has ruled for 32 years, after weeks of violence, military defections and political reversals.
Seeing political allies desert him en masse, the Yemeni leader agreed in principle to a proposal by GCC foreign ministers to step down in exchange for immunity from prosecution for himself, his family and top aides.
Read more: Protesters killed in Yemen shooting - Middle East - Al Jazeera English