Hundreds of activists in former Pakistani Prime Minister Nawaz Sharif's party have been detained and an arrest warrant was issued for Sharif's brother days before Sharif is due to return home from exile.
Sharif's supporters said the arrests were part of an effort to disrupt plans for mass rallies welcoming the former prime minister home on Monday.
A police official in Lahore acknowledged that officers had picked up 350 Sharif supporters, but a Sharif ally put the number at more than 1,000.
Sharif, who was toppled in a 1999 coup by Pakistan's President Gen. Pervez Musharraf, was convicted on charges of hijacking and terrorism and sentenced to life imprisonment before being released into exile in Saudi Arabia.
He has vowed to fly home from London on Monday to counter Musharraf's re-election bid and run for Parliament, despite veiled threats from senior officials to jail him.
"These are all cooked up, bogus cases to prevent Mr. Sharif and his brother from returning. We are determined to come back, and we will face these false charges in a court with our lawyers," said Nadir Chaudri, a spokesman for Sharif in London.
"Our objective is to block this military dictator from maneuvering and continuing his rule. We are going back to ensure that the rule of law is followed and democracy returns."
An anti-terrorism court in the eastern city of Lahore on Friday ordered the arrest of Sharif's younger brother, Shahbaz, in a murder case, said Aftab Ahmed Bajwa, a lawyer for the plaintiff.
Shahbaz Sharif is charged with ordering police to kill five men who were gunned down in Lahore in 1998. At the time of the killings, Shahbaz was the chief minister, or top executive, of Punjab province, and Nawaz was Pakistan's prime minister.
On Wednesday, the father of one of the victims asked the court to arrest Shahbaz Sharif since he is due to return to Pakistan, Bajwa said. Shahbaz Sharif has denied the allegation.
Meanwhile, an anti-corruption court in Rawalpindi, Pakistan, held a hearing in a case involving allegations that the Sharif family defaulted on a bank loan and owned property beyond their known financial means, said Zulfiqar Ahmed Bhutta, a prosecutor for the state National Accountability Bureau.
The cases date back to 2001 and 2002. Hearings were adjourned for years, but they were reopened late last month following an application by the government.
The judge set another hearing for Sept. 13 to ensure the Sharifs are in the country, Bhutta said.
Ahsan Iqbal, spokesman for Sharif's Pakistan Muslim League-N party, said the moves against the Sharifs "show complete panic in the ranks of the government."
Musharraf, a key ally in the U.S. war on terror, has seen his popularity decline since his failed attempt to fire the country's top judge earlier this year.
Musharraf has repeatedly said the Sharifs must remain in exile for 10 years under the terms of a deal reached in 2000, but the Supreme Court ruled last month they were free to enter Pakistan and that their return should not be obstructed.
Thousands of Sharif supporters are planning to converge on Islamabad to welcome him, but there are expectations that authorities will try to block them. The Sharifs plan to travel to Lahore, the capital of Punjab and their power base, by road.
Iqbal said more than 1,300 party supporters were arrested in raids on their homes across Punjab, which includes Islamabad airport, in the past three days.
"If the government uses illegal tactics and blocks them, that will increase political tension in the country and bring people onto the streets," he said.
Musharraf is expected to seek re-election by lawmakers by mid-October, but has yet to make a public commitment to resign as army chief if he continues as president. Many experts say that to keep his uniform - the main source of his power - beyond 2007 would violate the constitution.
To help smooth the way, Musharraf is trying to strike a deal with another exiled former prime minister, Benazir Bhutto, that could lead them to share power.
Bhutto has been pressing the pace of talks so that she can decide when to return.
However, Information Minister Mohammed Ali Durrani said Friday a final decision would come in the Muslim holy month of Ramadan, which begins in mid-September.
"The political process is moving forward. The government will not allow that political process to be disturbed," Durrani said.