By Mohammed Ghobari
SANAA (Reuters) - Yemen's opposition coalition vowed on Monday to escalate protests that have swept the country demanding the resignation of President Ali Abdullah Saleh, after he rejected a plan that would have him step down in 2011.
In the capital Sanaa's main prison, detainees rioted and confronted security forces who shot into the air in an attempt to regain control, a security official said.
"It was an attempt at a mass escape, and prisoners then turned to acts of sabotage," the official told Reuters, adding that riot police had surrounded the compound.
Tens of thousands of protesters are camped out in major Yemeni cities, staying awake through the night to hear speeches and sing national songs, as their tone against Saleh hardens.
Saleh, a U.S. ally against al Qaeda's Yemen-based wing, rejected a plan proposed by an opposition coalition last week, which would have implemented political and electoral reforms while paving the way for his resignation within the year.
"Recent events have proven that the regime is incapable of answering the demands of the people, and for that reason it needs to go," said the coalition's spokesman, Mohammed al-Sabry.
"The protesters are studying several options for an escalation, including organizing a day when all Yemenis will take to the streets, a 'Friday of No Return' protest, and other options," he told Reuters.
Yemen, neighbor to oil giant Saudi Arabia, was teetering on the brink of failed statehood even before recent protests. Saleh has struggled to cement a truce with Shi'ite Muslim rebels in the north and curb secessionist rebellion in the south.
The growing Yemeni protests, and a series of defections from Saleh's allies, have added to pressure on Saleh to end his three-decade rule in the Arabian Peninsula state. But neither side appears willing to compromise to end the deadlock.
Saleh rejected the opposition plan, which would have also required him to remove family members from key posts, and reiterated his pledge to resign when his term is set to expire in 2013. He also adopted a proposal by religious leaders for revamping elections, parliament and the judicial system.
Protesters are frustrated with corruption and soaring unemployment in Yemen, where 40 percent of its 23 million people live on $2 a day or less and a third face chronic hunger.
Half of Yemen's population is armed, and experts worry that as protests continue, sporadic clashes between Saleh loyalists and anti-government demonstrators could evolve into greater violence. The United States and Britain have warned citizens against travel in Yemen due to recent unrest.
(Additional reporting by Mohamed Sudam; writing by Erika Solomon; editing by Ralph Boulton)