Patients have been evacuated from a hospital in the Thai capital, Bangkok, after anti-government demonstrators forced their way into the grounds.
The red-shirts, looking for soldiers they thought were hiding there, later apologised for the incident.
In a TV address, Prime Minister Abhisit Vejjajiva has said he will not tolerate further violence by the reds, but gave no indication of any planned action.
The red-shirts are pressing the Thai government to call early elections.
Patients at the Chulalongkorn hospital were sent to other hospitals and all except emergency services had to be suspended after the brief incursion by about 100 red-shirts on Thursday night.
But the action was quickly disowned by the protesters’ leadership.
“On behalf of all leaders, I apologize to the public and Chulalongkorn hospital for the incident,” one of the red-shirt leaders Dr Weng Tojirakarn said.
“The situation got out of control. It is not our policy to obstruct hospital operations,” he said.