Bangkok, Thailand (CNN) -- At least eight people have been killed as Thai security forces declared a "live firing zone" in downtown Bangkok on Saturday following days of deadly clashes with anti-government protesters.
Saturday's fatality takes the total number of deaths to 25 since a government-backed clampdown on protesters exploded into violence on Thursday. More than 150 people have been wounded, according to emergency officials.
In a televised address, Thai Prime Minister Abhisit Vejjajiva said a small group of protesters among the opposition "Red Shirts" was trying to foment civil war.
The prime minister urged the citizenry to understand and embrace the government's stance. The country couldn't allow the rule of law to fail, he said, warning that the longer the protests continued, the higher the risk for the public.
"The government proposed a reconciliation plan but it was rejected," Abhisit said. "This benefits no one. It only benefits a small group which wants to harm the country and lead it to civil war. It is unbelieveble that they use peoples lives for political advantage."
Thousands of Red Shirts, who support ousted former prime minister Thaksin Shinawatra, have been occupying a central area of the city for weeks in a show of opposition to Abhisit.
The escalating unrest prompted the U.S. Embassy to issue a travel warning Saturday advising Americans to defer travel to Bangkok, spokeswoman Cynthia Brown told CNN.
Several other western embassies, including the UK, Japan, Canada, New Zealand and the Netherlands have also advised against travel to Bangkok.
Tensions remained high Saturday, with protesters yelling and screaming as they stood behind barricades of tires, spikes and bamboo poles.
But a military spokesman said security forces planned to put the protesters under more pressure Saturday as they cordoned off an area of several square kilometers, CNN's Sara Sidner reported.
"In the next few days, they will be stepping up their security measures," said Panitan Wattanayagorn, the acting Thai government spokesman.
Security forces rolled out razor wire and erected warning signs as they surrounded the area where the protesters have been clustered, CNN's Dan Rivers reported. He said Thai troops had also come under fire although it was unclear who was shooting at them.
"There's been quite a fierce gunfight where we are in the northwest corner of this zone that they have tried to surround a Ratchaprarop Road which has been declared a live fire zone by the army," said Rivers.
"There are signs up all along it warning residents to stay indoors, that there is live ammunition being used. We've been effectively pinned down while the army tries to deal with incoming fire. We're not sure who's firing on them but it's certainly been a very volatile situation with lots of explosions and gunfire going on."
Sidner, a few kilometers away inside the security force's cordon reported witnessing two people shot. Both appeared to be unarmed she said. Those present at the scene claimed rooftop snipers were responsible for the shootings, she said.
"The protesters clearly blame the army for the deadly force," said Sidner. "There is no way to know for sure who exactly is doing the shooting but neither of the people we saw injured were armed."
The Thai capital has been in chaos since Thursday, beset by gunfire, tear gas and stone-throwing that boiled over after Thai authorities set a new deadline to seal off the Bangkok intersection where protesters have gathered by the thousands for the past month.
A government official said Thai forces were slowly getting control of the downtown area, with video footage showing soldiers shooting rounds toward the area with protesters. Among those wounded on Friday was a journalist from a French television station who was shot in the leg.
The government said it was forced to take action after demonstrators disregarded an ultimatum by Prime Minister Abhisit Vejjajiva to vacate the intersection by Wednesday.
Wattanayagorn said Friday that security forces who have been the objects of attacks have no choice but to respond.
He told reporters that forces have been dutifully following the rules of engagement, which allow them to use live ammunition to protect themselves and their comrades. He assured Bangkok residents and foreigners that the forces have no intention of harming anyone.
The government, he said, is "very confident" it will be able to "stabilize the situation" and get it "under control very soon." Also, he said the prime minister is looking forward to working with others in hammering out reforms.
The United Front for Democracy, the formal name of the Red Shirt opposition, has been demanding that Abhisit dissolve the lower house of Parliament and call new elections. The Red Shirts support former Prime Minister Thaksin Shinawatra, who was ousted in a bloodless military coup.
Tensions ramped up when Maj. Gen. Khattiya Sawasdipol -- a renegade general better known as Seh Daeng, which means Red Commander -- was shot and wounded by a sniper's bullet Thursday, leaving him in critical condition.
Brown, of the U.S. Embassy in Bangkok, said that family members of embassy personnel had been offered voluntary departure. She said the embassy would remain closed on Monday and that staff were assessing the situation "day to day."
CNN's Dan Rivers and Sara Sidner contributed to this report.