Embattled president Hosni Mubarak has appeared on television for the first time since protests erupted demanding his ousting, and he said he will press ahead with social, economic and political reforms.
Mr Mubarak said he has asked his Cabinet to resign, and he called anti-government protests part of a plot to destabilise Egypt and destroy the legitimacy of his regime.
The president defended the security forces' crackdown on protesters.
Protesters have seized the streets of Cairo, battling police with stones and firebombs, burning down the ruling party headquarters, and defying a night curfew enforced by a military deployment.
US President Barack Obama later said he had spoken to Mr Mubarak and told him he has a responsibility to take concrete steps to deliver on promises of better democracy and greater economic opportunity. Mr Obama said: "This moment of volatility has to be turned into a moment of promise."
Earlier, Egypt's military deployed on the streets of Cairo to enforce a night-time curfew as the sun set on a day of rioting and violent chaos that was a major escalation in the challenge to authoritarian President Mubarak's 30-year rule.
Thousands in the capital still defied a nationwide curfew and were trying to storm two major government buildings - the state TV headquarters and the Foreign Ministry. Others were praying on the streets after nightfall.
Flames rose up across a number of cities from burning tyres and police cars. Even the ruling party headquarters in Cairo was ablaze in the outpouring of rage, bitterness and utter frustration with a regime seen as corrupt, heavy handed and neglectful of grinding poverty that afflicts nearly half of the 80 million Egyptians.
Hundreds were looting television sets and electric fans from the burning complex of buildings used by the ruling party.
One protester was killed in demonstrations that stretched across nearly half the provinces in Egypt, bringing the death toll for four days of protests to eight.