President Gen. Pervez Musharraf's government declared that it would block a 185-mile protest march Tuesday by opposition leader Benazir Bhutto. Her party said the march would proceed, setting up a perilous showdown between the two leaders.

Hundreds of armed police were deployed Monday in the streets around the home where Bhutto is staying, and sharpshooters took to surrounding rooftops. A series of three steel-and-barbed wire barricades were erected around her house.

A conflict over the march between Bhutto and Musharraf could intensify the political crisis engulfing Pakistan and further cloud the prospect of the two leaders forming a U.S.-backed alliance against rising Islamic extremism.

Bhutto was due to leave the eastern city of Lahore on Tuesday morning for the capital, Islamabad. The journey was expected to take about three days, and her party said thousands of supporters were expected to join her en route.

The caravan is meant to pressure Musharraf to end the state of emergency he imposed on Nov. 3 and also to give up his post as army chief.

"All processions, rallies, political gatherings at present are outlawed," Deputy Information Minister Tariq Azim told The Associated Press. "So if she breaks the law then obviously she will not be allowed to do it."

Azim declined to give details about what steps authorities might take against Bhutto. He said that officials would "take the necessary action as it happens."

Farhatullah Babar, a spokesman for Bhutto's Pakistan People's Party, said Tuesday's march would go ahead "regardless of what the government is saying."

Party spokeswoman Farzana Raja vowed its supporters would fight any attempt by authorities to block her "freedom march."

"If police try to stop us, in every town and district of Punjab, there will be a battlefield between PPP activists and police," she said.

With an escort of dozens of police vehicles, Bhutto ventured out around Lahore to offer prayers at the grave of Pakistan's national poet, Allama Iqbal, and declared to reporters that her caravan was part of her campaign "to save Pakistan."

"I know it is dangerous but what alternative is there when the country is in danger?" the former prime minister said.

Bhutto was targeted by an Oct. 18 suicide bombing attack on a homecoming procession in the southern city of Karachi as she returned from years in exile. The assassination attempt killed 145 other people.

She was placed under house arrest in Islamabad Friday to prevent her from addressing a rally in the nearby garrison city of Rawalpindi, where authorities also warned they had intelligence that suicide bombers were loose in the area.

Police said they had ramped up security around Bhutto again due to intelligence that a suicide bomber was planning to attack her in Lahore. Ayaz Salim, a top police official, said officers had searched all the city's hotels after receiving a tip that a suicide bomber was staying in one, but they did not find the suspect.

With Musharraf losing popularity due to growing disaffection in Pakistan over enduring military rule, the Bush administration backed talks about power-sharing between him and Bhutto as a way to keep a U.S.-friendly administration in control of the nuclear-armed nation where militants are orchestrating attacks inside the country, across the border in Afghanistan.

Foreign Ministry spokesman Mohammed Sadiq said Pakistan's nuclear weapons were secure and that there was no risk they would be seized by Taliban or al-Qaida-linked militants who have expanded their influence beyond northwestern border regions.

"There are multiple layers of command and control and the weapons are not in danger of falling into any hands," he said. "Pakistan's nuclear program is very well-guarded."

Musharraf has set no time limit on the emergency declaration, which has resulted in the arrests of thousands of his critics, a ban on rallies and the blacking out of independent TV networks. He said Sunday that the emergency was necessary to step up the fight against militants and ensure "absolutely fair and transparent elections" for parliament.

Since the imposition of emergency move came shortly before the supreme court was due to rule on the legality of his recent election for a new presidential term, Musharraf is finding it hard to shake suspicions it was actually a tactic to oust judges who could have obstructed his bid to extend his eight-year rule.

White House spokeswoman Dana Perino said that President Bush thinks emergency rule must be lifted "in order to have free and fair elections."

"But let me stress, the situation in Pakistan is evolving, and it's not easy predict," Perino added.

Bhutto has said the talks with Musharraf stalled because of the emergency declaration but could be revived if he rolls back emergency rule.

She joined other Pakistani opposition leaders in questioning whether a free and fair ballot would be possible under emergency rule. She welcomed Musharraf's commitment to holding elections on time in January, but likened campaigning under the emergency to being tied and blindfolded.

"In the prevailing circumstances you can't say the elections will be free and fair," she told reporters.

"Boycotting elections could be an option," she said. "We will consult the other political parties."

Other opposition parties already have threatened a boycott.

Bhutto also demanded that Musharraf step down as army chief when his current term as president expires Nov. 15 — a step he is promising to take once a reconstituted supreme court validates his recent presidential election victory.

Foreign ministers from the Commonwealth of Britain and its former colonies said that Pakistan would be suspended from the organization unless the state of emergency was repealed and Musharraf stepped down as army chief by Nov. 22.

"This affords Pakistan a last change to immediately address the issues," Maltese Foreign Minister Michael Frendo said.