“The solution to our current problems needs to start with the showing of responsibility,” Abhisit said. “The prime minister has never showed any responsibility or conscience.”
Abhisit also criticized Yingluck's Pheu Thai party for trying to amend a clause in the constitution that would have transformed the Senate into a fully elected body.
Currently about half its members are selected by a panel of judges and heads of independent state agencies.
The Constitutional Court sharply scolded Yingluck's party for the move.
The Democrats held 153 of the 500 seats in the lower house, according to the latest figures on their website.
In a speech Sunday, Yingluck said again that she was not trying to cling to power and would be “happy to resign” and dissolve Parliament if that could ease the crisis.
But she said those things could only happen if new elections are organized within 60 days and all parties accept the outcome.