Army chief General Anupong Paochinda will replace Deputy Prime Minister Suthep Thaugsuban, Mr Abhisit said, admitting that efforts to rein in the protests had failed six days after violent clashes killed 24 people.

"Brothers and sisters, I want to insist the government is going forward to solve the problem that we know brings sorrow to Thai people," Abhisit said in a televised address delayed from early afternoon.

"Many operations have failed because there has been a congregation of many people which presents obstacles and limitations to work of security forces ... Sometimes we have to be patient and sometimes we have to accept the impact of security operations."

The move comes after a failed attempt, ordered by Suthep, to arrest red shirt leaders on Friday, another embarrassing setback for the authorities after last week's failure to clear a protest site in the old part of the city.

Reuters