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A day after the Pakistani government deported former Prime Minister Nawaz Sharif, his supporters launched a formal protest with the Supreme Court on Tuesday but were largely prevented from taking their democracy movement to the streets by an aggressive security crackdown.

The court, which last month authorized Sharif’s return from exile, seems to be on a collision course with Pakistan’s president, Pervez Musharraf, following the government’s decision to deport the former prime minister Monday hours after he had arrived.

Sharif’s backers filed a petition Tuesday that alleges the government is in contempt of court.

The case is one of two the court is likely to hear in the coming days that could have vast repercussions for Pakistani politics. The other case challenges Musharraf’s eligibility to run for another term as president. By law, he must win another term this fall if he wants to stay in office, but his other job as army chief could disqualify him.

Sharif, deposed by Musharraf in a bloodless 1999 coup and in exile since 2000, had hoped to return to Pakistan to lead a campaign against the president.

His deportation raises questions about how well his party will be able to mobilize in his absence.

“Nawaz Sharif was illegally abducted, and the architect of this unlawful act is Gen. Pervez Musharraf,” Khawaja Asif, a senior official in Sharif’s party, said in a news conference on the white marble steps of the court.

Efforts to hold rallies in support of Sharif fizzled Tuesday.

The government enforced a ban against large gatherings, and many party members were shipped to remote detention centers after their arrests during the past several days.

“Our main leaders are all in jail,” Sardar Nasim, a politician with Sharif’s faction of the Pakistan Muslim League-Nawaz, told a small group of protesters in Rawalpindi. Police outnumbered demonstrators, and the rally broke up quickly.

The security crackdown continued on a day when a suicide bomber struck in northwestern Pakistan, killing 18 people.

The attack took place in Dera Ismail Khan, near the restive tribal area of Waziristan, and also injured 18 people, many of them critically.

“Local police spotted a suspicious boy and tried to get hold of him, but it was too late as he blew himself up in a crowded area,” said Mohammad Khaliq, the police chief.

Another police official said the suicide bomber was about 15 years old. Two security officers were among the dead.

The Taliban has been mounting an increasingly aggressive insurgency in recent months in northwestern Pakistan.

Last week, militants beheaded two women, accusing them of “immoral activities.”

A note found near the bodies warned that other women involved in similar activities would meet the same fate.

In a separate incident Tuesday, pro-Taliban militants made an unsuccessful attempt to destroy ancient Buddhist carvings by detonating a bomb in the Swat Valley.

The site attracts thousands of tourists every year.