CAIRO – Egyptian authorities launched an aggressive clampdown on foreign journalists and human rights activists Thursday as the government sought to shift the blame for the violence that has swept the capital.

In what the U.S. State Department called a “concerted campaign to intimidate,” several dozen journalists were rounded up by security forces and detained for hours, along with foreigners working as teachers, engineers and human rights researchers. Across the city, angry bands of supporters of President Hosni Mubarak also beat journalists; several reporters said that they had been threatened with death.

The remarkable sweep came as thousands of Mubarak opponents continued to gather in Tahrir Square, as they have for the past 10 days, demanding that the authoritarian ruler end his 30-year reign. They have planned another large demonstration for today. Prime Minister Ahmed Shafiq said late Thursday that the interior minister should not disrupt that gathering.

But the White House was nervously awaiting the renewed protests by anti-Mubarak demonstrators, worried that they could spark more violent clashes with Mubarak’s supporters. In an interview, Mubarak told ABC that he had told President Obama: “You don’t understand the Egyptian culture and what would happen if I step down now.”

Omar Suleiman, Egypt’s new vice president, suggested that the continuing clashes between Mubarak’s supporters and his critics had been instigated by people pursuing a “special agenda” — perhaps from abroad, perhaps from certain business interests, perhaps from the Muslim Brotherhood, Egypt’s oldest and best-organized opposition group. “They can be intermingled and interlinked,” Suleiman said.

Vice President Joe Biden later telephoned Suleiman, the White House said, to stress that “the Egyptian government is responsible for ensuring that peaceful demonstrations don’t lead to violence and intimidation.” The White House also said Egypt would be accountable “for allowing journalists and human rights advocates to conduct their important work, including immediately releasing those who have been detained.”

Among the journalists detained were two employees of The New York Times and four from The Washington Post. All of them had been released by early today.

A Dutch reporter was stabbed with a screwdriver, and security officers raided the Ramses Hilton hotel, near Tahrir Square, and confiscated transmission equipment from news organizations that had booked rooms there.

Others arrested included three journalists working for al-Jazeera, the satellite television station based in Qatar that has been a target of Mubarak’s wrath. In an apparent reference to al-Jazeera, Suleiman told Egyptian television: “I’m very sad about the behavior of these satellite channels that are associated with friendly countries. We feel their enmity.”

The effort by Egypt to turn the focus on what it regards as its critics came as violence continued to flare in and around Tahrir Square. Some anti-government protesters had converted the offices of a travel agency into a makeshift detention center, where they were holding captured Mubarak supporters.

Among their captives Thursday morning were two burly men who were stripped to the waist and seated on the floor; their captors said they had been caught with identification cards of the police or the ruling National Democratic Party. One of those detained yipped in pain as the protesters yanked upward on his arms, which were secured by flexicuffs.

“Drama queen,” one of the captors said. The captors said the prisoners would be turned over to the military once their identities were established.

“Our issue is simple: freedom and social justice,” said Hamad Othman Edeep, a 31-year-old teacher who was among those still encamped in the downtown square. He said he makes just under $100 a month, while Egypt’s rich grow ever wealthier. “How can I feed my children,” he said. “Do I have to be a thief?”

As the Egyptian unrest continued, U.S. officials were studying the components of the $1.5 billion annual U.S. aid package to Egypt, and the possibility that it could be used as leverage with the government. But most of the aid — $1.3 billion — is in the form of credits to purchase U.S. military equipment. Any cutoff would not only affect U.S. business but risk offending the Egyptian army, which the administration has praised for its nonpolitical conduct during the crisis.

Sen. Patrick Leahy, D-Vt., chairman of the Senate Appropriations subcommittee in charge of the aid, earlier in the week had called for the aid to be stopped if Mubarak did not resign. But Leahy tempered his remarks Thursday.

“I hope President Mubarak will realize that this violence threatens to blot his legacy,” Leahy said, “and that it will not prevent an early end to his rule, which now seems inevitable.”

Suleiman said Mubarak’s son Gamal, who had been considered a likely successor, would not be a candidate to succeed his father. The vice president also said he had begun holding talks with a variety of opposition figures in order to reach consensus on reforms, and that he had invited the banned Muslim Brotherhood to join in. But he insisted that it would take time to determine the proper reforms.

He thanked the young people who launched the protests here last week, but said their demand that Mubarak leave office before elections eight months from now was unreasonable.

Shafiq, the newly appointed prime minister, apologized for the violence of the past two days. Both he and Suleiman maintained that the government had nothing to do with the clashes, which began when supporters of the president poured into the center of Cairo on buses and launched an attack on Tahrir Square with a cavalry charge.

The Health Ministry said Thursday that eight people had been killed and more than 800 wounded in the two days of fighting.

“I don’t understand what has happened,” Shafiq said. “This is not the nature of the Egyptian people.”

“We need to know who was behind” the violent attacks at Tahrir Square, Suleiman said. “We will know. And they will be judged accordingly. Those people have actually spoiled and undermined President Mubarak’s work.”

Human Rights Watch said one of its American staffers, Daniel Williams, a former journalist, was among several rights workers taken into custody when police and army personnel raided the Hisham Mubarak Law Center.

Egyptian activists saw the targeting of the law center as evidence of a carefully planned attempt to weaken and discredit the pro-democracy movement. The center provides legal representation for a wide range of dissidents and political prisoners, and its lawyers were expected to help defend opposition figures who have been detained during unrest in the past two weeks.

Bahey Eldin Hassan, director of the Cairo Institute for Human Rights Studies, said the presence of foreigners at the offices of Egyptian human rights groups reinforces the view that Westerners are “collaborating against the government of Egypt.”