Opposition leader Benazir Bhutto on Tuesday called on President Gen. Pervez Musharraf to resign and ruled out serving under him in a future government after she was placed under house arrest for the second time in five days.

With the political turmoil deepening, Deputy Secretary of State John Negroponte was headed to Pakistan and expected to reiterate Washington's calls for Musharraf to lift the state of emergency.

Musharraf's critics and chief international backers, including the United States, have said the restrictions imposed by the military leader — such as on independent media and rallies — would make it hard to hold a fair vote in upcoming parliamentary elections.

The Bush administration is sending its No. 2 diplomat to Pakistan to tell Musharraf in person to rescind emergency rule and allow free and fair elections.

Deputy Secretary of State John Negroponte, now on a four-nation West Africa tour, will go to Pakistan by the end of the week to underscore U.S. concerns about the situation.

Bhutto was trapped in a padlocked house surrounded by thousands of riot police, trucks, tractors loaded with sand, and a row of metal barricades topped with barbed wire. She said it was now likely her Pakistan People's Party would boycott the January elections and ruled out serving another term as prime minister under Musharraf.

"I simply won't be able to believe anything he said to me," she told reporters by telephone from the house in Lahore where she was held to prevent her leading a protest procession.

Her comments appeared to bury hopes of the political rivals forming a pro-U.S. alliance against rising Islamic extremism. They had held months of talks that paved the way for Bhutto's return from exile last month to contest the parliamentary elections.

But Railways Minister Sheikh Rashid Ahmed, a close Musharraf ally, said he doubted Bhutto's had closed the door completely to any cooperation with the general.

"She talks one thing but walks in a different way," Ahmed said, saying her comments were a reaction to declining public support for her party. "She knows the election result will be different from what she thought. That is why she is trying to create a disturbance."

In the southern city of Karachi, Bhutto supporters fired on two police stations in a poor district where her party is popular, and police used tear gas to disperse demonstrators, senior police officer Fayyaz Khan said. A 9-year-old boy and a 22-year-old woman were wounded in crossfire between demonstrators and police, witnesses said.

Bhutto told the private Geo TV network that Musharraf was a hurdle to democracy and must resign both as president and army chief.

She accused Musharraf of imposing effective martial law when he declared emergency rule Nov. 3 — suspending citizens' rights and rounding up thousands of his opponents. Musharraf said the restrictions were needed to bolster the fight against the Taliban and al-Qaida.

Negroponte's trip to Pakistan was pre-planned and part of a regular strategic dialogue with Pakistan, a key ally in the U.S.-led war on terror, said U.S. Embassy spokeswoman Elizabeth Colton.

Authorities mounted a massive security operation to prevent Bhutto from leading a 175-mile procession to the capital of Islamabad to press for an end to emergency rule. Officers detained scores of her supporters, including several lawmakers, who approached the barricades shouting slogans including "Go, Musharraf, go!" and "Prime Minister Benazir!"

Bhutto's spokeswoman, Sherry Rehman, said the former prime minister was stuck in the house with a handful of top aides. She said Punjab's provincial government had attached the seven-day detention order as well as several padlocks to the front gate.

Aftab Cheema, chief of operations of Lahore police, said Bhutto would not be allowed to leave the house, which was declared a "sub-jail."

Bhutto said once she was freed from detention, she would work to forge a broad alliance including Nawaz Sharif — a longtime rival and fellow former prime minister who shares her wish to end military rule.

Sharif was ousted by Musharraf in the 1999 coup that brought the general to power. He tried to return to Pakistan in September but was immediately deported.

Speaking from exile in Saudi Arabia, Sharif told The Associated Press that he believed the opposition was "beginning to get together."

Bhutto said she saw no prospect of achieving political power by cooperating with Musharraf's administration.

"Now we've come to the conclusion that even if we get power, it will just be a show of power. It won't be substantive power," Bhutto said.

"It seems unlikely that the People's Party will participate in the upcoming elections," she said, describing the vote as a "stage-managed show" to return the ruling party to power.

Other Bhutto supporters went ahead with the procession without her.

Shah Mahmood Qureshi, president of Bhutto's party for Punjab, said he was leading a column of 200 vehicles from Lahore, but they had been stopped by police about 55 miles from the city and hundreds of people were detained. There was no immediate confirmation from officials of the arrests.

Police initially said they ramped up security around Bhutto due to intelligence that a suicide bomber was planning to attack her in Lahore.

Bhutto was targeted by an Oct. 18 suicide attack on a homecoming procession in the southern city of Karachi as she returned from years in exile. She was unscathed, but the blast killed 145 others.

She was put under house arrest in Islamabad on Friday to prevent her from addressing a rally in the nearby city of Rawalpindi, where authorities issued similar warnings.

With Musharraf losing popularity due to growing disaffection with military rule, U.S. officials encouraged him to reconcile with Bhutto in hope of keeping a U.S.-friendly administration in control of the nuclear-armed nation where militants are orchestrating attacks inside the country and across the border in Afghanistan.

Extinguishing that prospect would put extra strain on Musharraf's relations with Washington, which is also pressing him to quit his army post.

Musharraf, who took power in a 1999 coup and became a key U.S. ally in fighting al-Qaida and Taliban, has set no time limit for the emergency, which has also resulted in a ban on rallies and the blacking out of independent TV networks.

He signaled Sunday that he wanted to hold the elections with the restrictions in place, raising major doubts about the vote's credibility.

The emergency came shortly before the Supreme Court was due to rule on the legality of Musharraf's recent re-election for a new presidential term, and critics say it was a tactic to oust independent-minded judges and prolong his eight-year rule.