LAHORE, Pakistan — A senior official said Wednesday that Benazir Bhutto will remain under house arrest for at least another day, while the Bush administration sent its No. 2 diplomat to Pakistan to urge President Gen. Pervez Musharraf to rescind emergency rule.

Meanwhile, another opposition leader was arrested after he showed up at a student rally in Lahore, police said. Imran Khan, a cricket legend who leads a small but outspoken opposition party, was the only one of Musharraf's most outspoken critics not in detention or exile.

Authorities put Bhutto under house arrest Tuesday for the second time in a week, and a senior federal government official told The Associated Press that she was grounded until at least Thursday.

"The position for her will remain like this until at least tomorrow. Then the government will review what to do with her," the official said on condition of anonymity because the matter was politically sensitive and no decision had been made to release her.

Bhutto said Tuesday she was working to forge a partnership with Nawaz Sharif, the man overthrown as prime minister in a 1999 coup by Musharraf. She demanded that Musharraf step down, dashing Western hopes the two moderate leaders would form an alliance to confront strengthening Islamic extremists.

Bhutto's call, which could see Pakistan's two main opposition parties joining, raised a new threat for Musharraf, a key U.S. ally who faces growing pressure at home and abroad to end emergency rule and restore democracy.

It further complicated matters for Washington, which has criticized Musharraf's recent crackdown on dissent but sees him as a dependable partner against al-Qaida.

Deputy Secretary of State John Negroponte was expected in Pakistan on Friday to underscore U.S. concerns about the situation, where rallies have been banned and independent TV news blacked out.

"We continue to want to see elections move forward in a free, fair and transparent manner (and) we want to see the emergency decree lifted," deputy State Department spokesman Tom Casey said. "We want to see all moderate political forces be able to work together.

However, Bhutto said she could not work with Musharraf.

"The international community needs to decide whether it will go with one man or the people of Pakistan," Bhutto told the AP by telephone Tuesday from the house where she is being held in the city of Lahore.

Musharraf says emergency rule is needed to curb political unrest that he says is hampering the government's fight against militants along the border with Afghanistan.

Critics contend the Nov. 3 emergency decree was a cover to oust independent-minded judges who had crimped Musharraf's powers. They call his move outright martial law since authorities have unchecked power to detain opponents.

Khan, who had been in hiding since escaping from house arrest a day after emergency rule was declared, was promptly detained by hardline students and handed over to police Wednesday, authorities said.

Some 200 student supporters cheered wildly and lifted Khan into the air when he got out of a car on a university campus in Lahore, but other students representing the hard-line Jamaat-e-Islami party surged forward, grabbed Khan and handed him over to police, senior police official Aftab Cheema told the AP.

Cheema said Khan is being held at an undisclosed location, and was charged under the Anti-Terrorism Act. He gave no details of specific charges, but said Khan was disturbing the peace.

"He created a law and order situation at the educational institution and caused a disruption in educational activities," Cheema told AP.

Jamaat-e-Islami is also opposed to Musharraf's declaration of emergency rule, but the students apparently were angered that the relatively moderate Khan was allowed on campus.

Bhutto, a secularist who has served as prime minister twice, is trapped in a padlocked house surrounded by hundreds of police. Approach roads are blocked with trucks and metal barricades lined by barbed wire.

Her detention prevented her from staging a protest procession to the capital, Islamabad. The procession went ahead but was quickly stopped by police, and security forces also clashed with anti-government protesters in other cities.

"Musharraf knows how to crack down against pro-democracy forces," Bhutto wrote in an op-ed piece published Wednesday in the Washington Post. "He is, however, unwilling or unable to track down and arrest Osama bin Laden or contain the extremists. This is the reality of Pakistan in November 2007.

"The only terror that Musharraf's regime seems able to confront is the terror of his own illegitimacy," she added.

Musharraf on Tuesday rejected Bhutto's call to resign as well as an appeal by Secretary of State Condoleezza Rice to lift the state of emergency.

"I totally disagree with her," Musharraf said of Rice in an interview in Islamabad with The New York Times. "The emergency is to ensure elections go in an undisturbed manner."

Musharraf also said that Bhutto was exaggerating her popular support. "Let's start the elections and let's see whether she wins," Musharraf told the Times.

Bhutto said she would work to forge an opposition alliance including Sharif, a longtime rival and former prime minister also trying to make a political comeback.

Sharif returned to Pakistan in September to prepare for January parliamentary elections but was immediately deported despite a Pakistani Supreme Court ruling that he could stay.

Speaking to the AP from exile in Saudi Arabia, Sharif welcomed Bhutto's comments and urged opposition parties to unite to "fight dictatorship."

Musharraf has set no time limit for emergency rule. He signaled Sunday that he wants to hold elections while keeping his ban on rallies and suspension of other rights, raising major doubts about the vote's credibility.

Associated Press writers Matthew Rosenberg in Lahore and Stephen Graham and Matthew Pennington in Islamabad contributed to this report.