ISLAMABAD, Pakistan — Pakistani police placed opposition leader Benazir Bhutto under house arrest today, uncoiling barbed wire in front of her Islamabad villa, and reportedly rounding up thousands of her supporters to block a mass protest against emergency rule.

The United States called for the restrictions on Bhutto to be lifted, saying it was “crucial for Pakistan’s future that moderate political forces work together to bring Pakistan back on the path to democracy.” A government spokesman promised she would be free by Saturday.

Bhutto twice tried to leave in her car on today, telling police: “Do not raise hands on women. You are Muslims. This is un-Islamic.” They responded by blocking her way with an armored vehicle.

The former prime minister had planned to defy a ban on political gatherings and address a rally in nearby Rawalpindi, where police used tear gas and batons to chase off hundreds of supporters who staged wildcat protests and hurled stones. More than 100 were arrested.

The city mayor said they had reports suicide bombers might attack the rally. Deputy Information Minister Tariq Azim said there was a restraining order against Bhutto, telling her to stay at her Islamabad home and not proceed to Rawalpindi because of the security threat.

“I expect that (the order) is all over by now,” Azim told The Associated Press. “She will be free to move tomorrow.”

President Gen. Pervez Musharraf came under increased pressure from his chief international supporter, the United States.

“We remain concerned about the continued state of emergency and curtailment of basic freedoms and urge Pakistani authorities to quickly return to constitutional order and democratic norms,” Gordon Johndroe, a spokesman for the National Security Council said in a statement. “Former Prime Minister Bhutto and other political party members must be permitted freedom of movement and all protesters released.”

Defense Secretary Robert Gates, speaking to reporters earlier today on his plane en route home from a weeklong visit to Asia, said he was concerned Musharraf’s emergency declaration and the protests and arrests that it spawned could affect operations in Afghanistan.

“The concern I have is that the longer the internal problems continue, the more distracted the Pakistani army and security services will be in terms of the internal situation rather than focusing on the terrorist threat in the frontier area,” said Gates.

Further afield, a suicide bombing at a government minister’s home in the northwestern city of Peshawar killed four people. Minister for Political Affairs Amir Muqam was unhurt.

The attack underscored the threat posed by religious extremists in this Islamic nation that Musharraf and Bhutto are sparring over. It was cited by Musharraf as the primary reason for imposing the state of emergency last Saturday.

But most of the thousands of people rounded up countrywide since have been moderates — lawyers and activists from secular opposition parties, such as Bhutto’s Pakistan People’s Party. The mass detentions have fueled criticism that Musharraf — who seized power in a 1999 coup — declared the emergency to maintain his own grip on power.

Friday’s crackdown showed that Musharraf was not letting up on his political rivals, despite saying a day earlier that parliamentary elections would go ahead by mid-February, just a month later than originally planned.

But the crackdown further dimmed prospects that Bhutto and Musharraf would form an alliance, which Washington has pushed for, against Islamic extremists.

Speaking to a few dozen supporters inside the barricades after her second foiled attempt to escape, Bhutto said that “we suspended our negotiations” with Musharraf after the emergency was imposed. She also repeated demands that Musharraf step down as army chief by next week.

Musharraf’s popularity has plummeted this year amid growing resentment of military rule and his government’s failure to curb Taliban and al-Qaida militants.

Outside Bhutto’s house at least 30 supporters were arrested, including a woman who showed up with flowers.

An old bearded man who showed up with a sharp machete and a goat he planned to sacrifice to bring Bhutto good luck was simply shooed away by police.

There was confusion over whether authorities had served Bhutto with a formal detention order. Officials said they had, but Bhutto’s aides said they had not received it — and would not accept it. An intelligence official, speaking on condition of anonymity because he was not authorized to speak to media, said Bhutto was ordered detained for 30 days, but Azim denied that.

After being turned back twice, Bhutto delivered an address heard by reporters on the other side of the barricades.

“I want to tell you to have courage because this battle is against dictatorship and it will be won by the people,” she told her followers.

Her supporters said they would only be further emboldened by Friday’s clampdown.

“We are going to besiege” Islamabad, said Abida Hussain, a former ambassador to the United States. “Our party activists have been mobilized to move out and take to the streets.”

Authorities appeared determined to stop them. Bhutto’s Pakistan People’s Party, or PPP, claimed Friday that 5,000 of its supporters had been arrested in the last three days across the eastern province of Punjab. But security officials said only 1,100 had been detained.

In Rawalpindi, the normally bustling city near Islamabad where Bhutto had planned to hold her rally Friday, hundreds of police — some on horseback, motorcycles or in armored vehicles — kept a tight grip on the largely empty streets and moved fast against any hint of protest.

Rawalpindi’s mayor had earlier in the day warned of a “credible report” that six or seven bombers were preparing a repeat of last month’s attack of Bhutto’s jubilant homecoming procession in the southern city of Karachi after eight years of exile. She escaped unharmed, but more than 145 people died in the attack, blamed on Islamic militants.

Rawalpindi has also been hit by a series of suicide attacks, targeting the military.

There were also scattered protests in Peshawar and Karachi, where opposition supporters blocked some roads with burning tires.

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Associated Press writers Stephen Graham in Rawalpindi, Riaz Khan in Peshawar and Munir Ahmad in Islamabad contributed to this story.