WASHINGTON (AP) — The United States on Thursday severely criticized what it called systematic attacks on journalists in Egypt and said they appeared to be an attempt to shut out reporting of even bigger anti-government demonstrations to come.

Secretary of State Hillary Rodham Clinton condemned “in the strongest terms” the pro-government mobs that beat, threatened and intimidated reporters in Cairo.

Attacks as well on peaceful demonstrators, human rights activists, foreigners and diplomats were “unacceptable under any circumstances,” she said.

Clinton pointed the finger at the government of Egypt’s 82-year-old president, Hosni Mubarak, without explicitly blaming it for the violence. She said, “It is especially in times of crisis that governments must demonstrate their adherence to these universal values,”

Egypt’s government must hold accountable those responsible for the attacks and “must demonstrate its willingness to ensure journalists’ ability to report on these events to the people of Egypt and to the world,” she said.

Foreign photographers reported attacks by Mubarak supporters near Tahrir Square, the scene of vicious battles between Mubarak supporters and protesters demanding he step down after nearly 30 years in power.

The Egyptian government has accused media outlets of being sympathetic to protesters who want Mubarak to quit now rather than complete his term as he has pledged.

Among the many detained were correspondents for The New York Times, Washington Post and Al-Jazeera. Human rights groups said many activists also were taken away after a raid by the military police on a legal center in Cairo.

The Obama administration warned that the arrests and intimidation of reporters may be aimed at stopping the spread of the anti-government message ahead of a potentially critical protests Friday, when many Egyptians are expected to take to the streets after prayer services.

“It could well be that this is in anticipation of events tomorrow,” State Department spokesman P.J. Crowley said. “We are bracing for a significant increase in the number of demonstrators on the streets and . the real prospect of a confrontation.”

White House spokesman Robert Gibbs also offered a strong denunciation of reported “systematic targeting” of journalists. He said, “I think we need to be clear that the world is watching the actions that are taking place right now in Egypt.”

On Capitol Hill, the Senate approved a non-binding resolution late Thursday urging Mubarak to hand over power to a caretaker government and begin a peaceful transition to a democratic society.

Amid heightened U.S. concern about rising violence in Egypt, President Barack Obama began his remarks at Thursday’s National Prayer Breakfast with pointed hopes for better days ahead: “We pray that the violence in Egypt will end and the rights and aspirations of the Egyptian people will be realized.”

And the administration complained Mubarak’s government was failing to immediately start a process toward real democracy, continuing the U.S. pressure on its once strong ally to accept the call of hundreds of thousands of demonstrators over the past week for democratic change.

Clinton said the government needed to engage a “broad and credible representation of Egypt’s opposition” in “serious negotiations on a peaceful and orderly transition.”

The comments followed Wednesday’s attack on protesters in Cairo’s main square by hundreds of pro-government supporters, some riding horses and camels and wielding whips.

In Egypt, Prime Minister Ahmed Shafiq acknowledged that the assault “seemed to have been organized.” He promised an investigation.

Crowley blamed elements close to the government or ruling party for instigating the violence, though he said it was still unclear how high up the order came from.

The administration’s call for an immediate transition from three decades of authoritarian rule in Egypt has coincided with American hopes that reforms in Jordan and Yemen could stave off similar revolt.

All three countries have experienced instability since protesters in Tunisia chased their leader from power last month.

Obama telephone Yemen’s President Ali Abdullah Saleh to welcome “significant reform measures” that Saleh’s government announced.

The White House said Thursday that Obama also stressed that Saleh “now needs to follow up his pledge with concrete actions,” and urged that security forces show restraint in dealing with protests.

Obama also urged forceful action against al-Qaida, which has turned the impoverished Arabian country into one of the main battlegrounds in the war on terror.

Clinton had a 15-minute phone conversation with Jordan’s King Abdullah II to tell him the United States looked forward to working with his newly named prime minister and Cabinet.

“We are eager to continue to support Jordan during these difficult times,” Crowley said. “We appreciate the example that Jordan has set in allowing freedom of expression during recent protests.”

Separately Thursday, a senior intelligence official said Obama was warned of instability in Egypt “at the end of last year.”

CIA official Stephanie O’Sullivan would provide no further detail during an open Senate confirmation hearing to be the deputy director of national intelligence.

The chairwoman of the Senate Intelligence Committee, Dianne Feinstein, D-Calif., told The Associated Press that the events “should not have come upon us with the surprise that they did.”

She said the Internet’s use in organizing demonstrations in Tunisia and Egypt should have provided “much more warning,” and that her committee would look into how intelligence agencies performed.

“Was someone looking at what was going on the Internet?” she asked.

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Associated Press writer Kimberly Dozier contributed to this report.