He described the audio tape as a "dirty trick" originating from a former prime minister's network.
"It is unbelievable. This method can risk causing confusion and violence within the country. I will take legal action against people who did it," Abhisit said.
"The audio clip was definitely doctored because I can confirm I have never issued any such instruction on crowd control," he said.
He was reacting to an audio clip circulated on the Internet in which a voice like his instructs security forces to use violence against red-shirt protesters during the April chaos, so that the government could impose an emergency decree to control the situation.
The red shirts claimed the audio clip is evidence of Abhisit's attempt to incite mayhem as a pretext to declare a state of emergency.
Deputy Premier Suthep Thaugsuban said the doctored audio clip was aimed at inducing hatred towards the prime minister.
PM's Office Minister Satit Wongnontaey said after listening to the clip that the prime minister did not make such an order during the volatile political situation in April.
Chuan Leekpai, former Democrat Party leader and the chief party adviser, also vouched for Abhisit, saying he believed the prime minister would never speak that way.
Abhisit admitted the voice at the beginning of the clip belonged to him, but that part of the content was not what he had said.
"The audio clip was edited because the levels of sound were different," said the prime minister, "I affirm that I have never said these words in such a combination."
The premier said his policy to deal with the so-called red shirt protesters is clearly based on the rule of law and respect for human rights.
Abhisit said he was ready to clarify any doubts regarding the audio clip and blamed those behind it of intending to hurt the country and incite violence. He also warned such audio editing could be illegal. The premier said he had clues some people who disseminated the clip belonged to a political party with close ties to a former prime minister's network. They must be held responsible if the audio clip was proven to be edited, he said.
"It's incredible they used dirty tactics to cause disturbances in the country," said Abhisit, "I will take legal action against those involved."
The prime minister said he had instructed national police chief General Patcharawat Wongsuwan to check the authenticity of the clip and its source.
Special Branch commander Police Lt-General Theeradej Rodphothong said he expected the examination result soon. He said the Special Branch is now checking who had released the clip, saying it was first aired at a red-shirt rally in Udon Thani province.
"It is still unconfirmed whether the voice heard in the clip is the premier's," said Theeradej, admitting that "if the clip is not real, it is seamlessly edited."
Meanwhile, Jatuporn Prompan, an opposition Pheu Thai Party MP and key red-shirt leader, said the prime minister and his Cabinet should resign if the clip turned out to be authentic.
Jatuporn said he had listened to the clip some time ago and said he prayed it was not the voice of the prime minister. However the speech was so smooth it sounded authentic.
He added the opposition party would not have accused the premier, as the use of a 'dirty tactic' is not its style.
The Pheu Thai MP said he had no idea who was behind the clip, but that Abhisit must be aware what he had said and to whom. "Abhisit must prove his claims the clip was edited," said Jatuporn.