The red-shirted United Front for Democracy against Dictatorship (UDD) was forced into a humiliating apology after its raid prompted severe criticism.

Weng Tojirakarn, a red shirt leader and medical doctor, apologised for the raid, calling it “inappropriate, too much, and unreasonable''.

Assistant national police chief Worapong Chiewpreecha said the search at Chulalongkorn Hospital by the red shirts threatened patients, relatives, and medical personnel.

The government's Centre for the Resolution of the Emergency Situation (CRES) ordered police to ensure that all hospitals are safe places.

The Royal Thai Police will deploy police to secure all hospitals and more than 100 police will guard Chulalongkorn Hospital, which was searched by red shirt protesters led by Payap Panket on the night of April 29.

They suspected the hospital was sheltering soldiers, but their search turned up nothing.

Deputy Bangkok police chief Amnuay Nimmano promised police would arrest Mr Payap when they had the chance.