ISLAMABAD, Pakistan - Lawyers for former Prime Minister Nawaz Sharif went to the country's highest court on Tuesday to challenge his deportation, setting up another confrontation between the judiciary and the U.S.-backed military ruler struggling to hold power in Pakistan.

President Gen. Pervez Musharraf sent Sharif, the premier he ousted in a 1999 coup, back into exile on Monday after the opposition leader landed on a flight from London. Sharif, who had vowed to return home to campaign against Musharraf, was also charged with corruption during his four-hour stay in the country.

Sharif's lawyers petitioned the Supreme Court to hold the government in contempt in relation to the deportation to Saudi Arabia. Last month, the court ruled that Sharif had an "inalienable right" to return home and that authorities should not obstruct him.

"We will fight this battle in the court of law," Sharif's nephew, Hamza Sharif, told reporters on the steps of the Supreme Court after the petition was filed. "We are fully confident that we will win, God willing."

Interior Ministry spokesman Javed Iqbal Cheema denied any wrongdoing, but said the government would respond to the petition if the court accepts it.

In two towns in eastern Pakistan, several hundred people protested the deportation and the government of Musharraf, who has allied himself closely with the United States since the Sept. 11, 2001, attacks.

About 200 members of Sharif's party and other opposition groups blocked traffic on a road in Lahore, chanting slogans including, "America has a dog in uniform," a reference to Musharraf.

The Supreme Court has emerged as a check on Musharraf's dominance since his failed attempt to fire the country's top judge earlier this year that sparked a nationwide protest movement.

It is already hearing petitions challenging Musharraf's holding of the post of army chief and president simultaneously and his eligibility to contest upcoming presidential elections. Judges are also pressing the government to provide information about the fate of hundreds of people allegedly held by Pakistan's shadowy intelligence agencies on accusations of terrorism and anti-government activities.

Analysts say Monday's decision to expel Sharif will deepen Musharraf's unpopularity in Pakistan and reinforce impressions that he is an authoritarian leader. It could also undermine the legitimacy of legislative elections due by January 2008.

The political crisis has unfolded as Musharraf struggles to stabilize Pakistan's volatile northwest, near the Afghan border, where Islamic militants have stepped up their campaign against the government

On Tuesday, a suicide bomber blew himself up near a pickup truck carrying passengers, killing up to 18 people, officials said.

The bomber boarded the truck as it traveled to a village near the city of Dera Ismail Khan after he was challenged by police who thought he was acting suspiciously, said Habibur Rehman, the district's police chief.

When police stopped the truck and the suspected bomber was asked to come down to be searched, he detonated the explosives strapped to his body, said city councilor Malik Khan Zaman. Two police were among the dead, he said.

Interior Ministry spokesman Brig. Javed Iqbal Cheema said 16 people were killed. Ahsan Waheed, a doctor at a local hospital where the victims were taken, said 18 were killed.

Witnesses said the bomber appeared to be in his early teens.

Ali Ahmed Kurd, a senior member of the Pakistan Bar Council, said lawyers across the country were boycotting court proceedings to protest Sharif's deportation. At one of the protests, in Karachi, lawyers were also protesting the shooting of a colleague they said was targeted because of his opposition to the government.

"The system is based on the crutches of a uniformed president, and the day these crutches are removed the present political system will collapse," wrote Urdu-language newspaper Nawa-I-Waqt in an editorial, one of several that judged the move to exile Sharif was an act of desperation by Musharraf.

Deputy Information Minister Tariq Azim told the British Broadcasting Corp. that the government obeyed the Supreme Court ruling to let Sharif enter the country, but that the former premier chose to go back into exile to avoid facing trial.

Sharif was originally exiled in 2000 following the coup. Accused of denying landing rights to a plane carrying Musharraf that was short on fuel, Sharif was jailed but later released and sent to Saudi Arabia after allegedly pledging not to return for a decade.

"No hindrance or obstacle was placed upon his entry into Pakistan," Azim told the British Broadcasting Corp.

Sadiq ul-Farooq of Sharif's Pakistan Muslim League-N party rejected Azim's claim as a "baseless concoction" and insisted that Sharif had volunteered to be arrested by police at Islamabad airport after he was served a warrant.

He estimated that more than 5,000 Sharif party workers and leaders have been arrested nationwide in recent days, including the party's chairman and former Pakistani President Rafiq Tarar.

The Interior Ministry said about 1,000 people were taken into custody. Asked when they would be released, Cheema said their cases would be handled under the law.

"Our leadership is in jail now. We are in a complete disarray," said Khawaja Mohammed Asif, a lawmaker from Sharif's party.