Prime Minister Abhisit Vejjajiva, whom the protesters seek to overthrow, went on nationwide television to criticize recent Red Shirt actions that have paralyzed areas of central Bangkok.
The Red Shirts, drawn mostly from the rural and urban poor, are demanding dissolution of Parliament and new elections, saying Abhisit came to power through the connivance of Bangkok's elite bureaucrats and the military, which ousted their hero -- ex-Prime Minister Thaksin Shinawatra -- in a 2006 coup.
"It's not necessary for me to condemn (the hospital break-in) since Thai society and the world community have already done that," Abhisit said, adding that the government would "not allow any movements that pose threats to the public."
Despite such warnings, the Red Shirts have defied authorities at every turn, entering the Parliament building, laying siege to a telecommunications complex, blocking roads and staging mass motorized rallies since setting up camp in the capital March 12. At least 27 people have died and nearly 1,000 have been injured in outbreaks of street violence.
Security forces have in almost every instance been unable or unwilling to stop the Red Shirt forays, including the incursion into the century-old public hospital, which feared a second break-in Friday.
However, Weng Tojirakarn, a Red Shirt leader and medical doctor, issued a "deep apology" for the raid staged by up to 100 protesters. He called it "inappropriate, too much, and unreasonable."
Later, the protesters opened up a section of their barricade to allow vehicles access to one of the entrances to the Chulalongkorn Hospital compound.
It was not clear whether Weng apologized because of the sharp negative reaction, or whether the foray was staged by some of the more radical Red Shirts rather than by general consensus.
About 100 police were sent to guard the hospital grounds. A hospital announcement said patients were sent to other hospitals or to buildings farther away from the Red Shirts. Almost all outpatient services were being suspended along with surgery, except in emergency cases.
"They can protest all they want but they should not come here, and they should not have prevented us from receiving service," said an angry Purin Supadith, one of many being turned away at the hospital's outpatient department Friday morning.
In the face of such incidents, Thai pro-establishment activists have demanded military action against the protesters and an end to "anarchy" in the capital.
The re-emergence of the so-called Yellow Shirts -- notorious for shutting Bangkok's airports for a week in 2008 -- added to the volatility on the streets of Bangkok.
The unrest is the result of a political standoff over the 2006 military coup that ousted populist prime minister Thaksin on corruption allegations.
The crisis has hurt business in the capital and devastated Thailand's vital tourist industry, which accounts for 6 percent of the economy.
But Finance Minister Korn Chatikavanij said Friday the economy as a whole is still faring well, with high foreign exchange reserves.
"The Thai economy is showing great resilience. So I think we can survive this. We'll have no problem staging a quick and immediate rebound," Korn said.
The Central Bank on Thursday raised its growth forecast for 2010 on the expectations of stronger exports as the global economy improves. It now expects economic growth in a range of 4.3 percent to 5.8 percent, compared with an earlier forecast of 3.3 percent to 5.5 percent.
Parts of Bangkok's commercial heart have become a barricaded Red Shirt protest camp. The "occupied zone" flanks Chulalongkorn Hospital and abuts the Silom Road financial district, now a campground for military and police units.