Egyptian opposition figure Mohamed ElBaradei warned of the risk of a bloodbath after clashes in Cairo on Wednesday between opponents and supporters of President Hosni Mubarak.
ElBaradei repeated his call for Mubarak to step down immediately and accused the government of using "scare tactics" to try to cling on to power.
"I'm extremely concerned, I mean this is yet another symptom, or another indication, of a criminal regime using criminal acts," ElBaradei told BBC radio from Cairo, when asked about the clashes.
"My fear is that it will turn into a bloodbath," he added.
The fighting broke out as international pressure grew on Mubarak to quit and his closest ally, the United States, told him bluntly that a political transition must begin immediately.
Mubarak went on national television on Tuesday night to say he would not stand in elections scheduled for September, but ElBaradei repeated his call for him to go at onc and dismissed concessions offered by the president.
"It seems to me that this is a regime that does not want to listen to the people, does not want to understand that they need to go, and in fact it strengthens the resolve of every Egyptian that Mr Mubarak has to go, has to go immediately before the country goes down the drain."
ElBaradei accused the government of encouraging clashes to try to end mass protests which have engulfed central Cairo over the past week.
"Now they want to get rid of millions of people who are demonstrating, and will continue to demonstrate, by scare tactics," he said.
ElBaradei said there was no reason to wait until elections scheduled for September for a change of ruler.
"Even if I take him on his word, why do I have to keep a representative of a regime which I believe is turning into a regime of thugs?
"Why do Egyptians have to keep him for seven months of instability, of insecurity, of intimidation?" he said.