Washington, Jan 27 (Agencies): Taking stern view on political upheaval and brutal crackdowns in Egypt, the US asked the government to respond to its people's yearnings for democracy as the largest political protests in years swept Cairo streets.

But with no clear picture emerging of a democratic and pro-Western alternative to the three-decade rule of Egypt's authoritarian President Hosni Mubarak, it was unclear how hard the United States was willing to press its case.

A day after delivering a measured response to Egypt's demonstrations, Secretary of State Hillary Rodham Clinton said on Wednesday that Egypt had to adopt democratic and other reforms and allow peaceful protests.

She told Cairo to lay off social media sites like Facebook and Twitter even as activists are using them to organise street gatherings and destabilise the government.

The White House declined a direct opportunity to affirm support for Mubarak, who travelled to Washington to meet President Barack Obama just four months ago.

Asked if the administration still backed Mubarak, White House spokesman Robert Gibbs would say only: "Egypt is a strong ally."

The tougher tone came as the US struggles to confront an explosion of instability in the Middle East as Arabs from Tunisia to Yemen rebel against decades of political repression.

Adding to the confluence of crises is the emergence of an Iranian-backed militant movement as Lebanon's dominant force and potentially embarrassing revelations creating new obstacles to Israeli-Palestinian peace.

Clinton said Mubarak's government had the power to ease tensions with anti-government activists, who defied an official ban on protests on Wednesday by pelting police with firebombs and rocks in a second day of clashes.

Police forces used tear gas and fired live ammunition in the air to disperse demonstrators. Some people were beaten.

"I do think it's possible for there to be reforms and that is what we are urging and calling for," Clinton told reporters at a State Department news conference with visiting Jordanian Foreign Minister Nasser Judeh.