LAHORE, Pakistan – 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.

The Bush administration offered a measured response to Bhutto’s remarks.

“We remain concerned … (but) we are hopeful that moderate elements would join together,” White House spokeswoman Dana Perino said. Pakistan should get back on a path to democracy and “the political parties in Pakistan should all be working together toward that goal,” she said.

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

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 a 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 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.

In an interview with The New York Times on Tuesday, Musharraf said Bhutto “has no right” to ask him to resign, and said she was exaggerating her popular support.

“Let’s start the elections and let’s see whether she wins,” Musharraf said.

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.

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

Associated Press writers Zarar Khan in Lahore and Matthew Pennington in Islamabad contributed to this report