Spokesman Robert Gibbs said they had yet to take the "necessary steps" the country's people needed to see.

Wednesday saw protests in the capital Cairo spread to the parliament.

There are reports of widespread industrial action, and of protests outside Cairo turning violent.

The Egyptian government has announced plans for a peaceful transition which see President Mubarak staying in office until elections in September, but opposition groups fear the government is stalling for time and will fail to enact meaningful changes.

Mr Gibbs said: "The government has not taken the necessary steps that the people of Egypt need to see. That's why more and more people come out to register their grievances.

"If there's some notion on the government side that you can put the genie back in this bottle, I think that's gone a long time ago."

He added that the US was reviewing its aid programme to Egypt, and the government's restraint and reform would determine "what that aid will look like".

His remarks follow Tuesday's call by US Vice-President Joe Biden for the Egyptian government to lift its longstanding state of emergency, and to stop harassing journalists and activists.

The Obama administration is clearly ratcheting up the pressure.

However, Egyptian Foreign Minister Ahmed Aboul Gheit has welcomed the US administration's current approach, while warning against attempts to impose its will on his government.