The request came from the Centre for the Administration of Peace and Order (Capo), he said.
Gen Winthai said soldiers and police began taking up positions on Friday night at key sites in the capital, including Government House, Suvarnabhumi airport, the headquarters of television channels 3, 5, 7, 9, NBT and Thai PBS, the Metropolitan Waterworks Authority and the Metropolitan Electricity Authority, since Friday night.
The presence of soldiers at the TV stations led to the spread of romours on social media that a coup was being planned. The rumours were quickly dismissed as baseless.
The government has said that around 20,000 police and soldiers would be deployed to protect property and guard against violence.
The People's Democratic Reform Committee (PDRC), led by former Democrat MP Suthep Thuagsuban, plans to "shut down" Bangkok on Monday by rallying at seven main areas in the capital, to pressure caretaker Prime Minister Yingluck Shinawatra and her ministers to step down.