The government has reopened corruption cases against former Prime Minister Nawaz Sharif, and a court on Friday ordered the arrest of his brother, three days before their return to Pakistan to challenge its military leader, lawyers said.

Sharif's party denounced the cases as politically motivated and claimed police had detained 1,300 of its workers to stop them welcoming the brothers home, ratcheting up political tension.

Nawaz Sharif was toppled by President Gen. Pervez Musharraf in a 1999 coup and sent into exile in Saudi Arabia. He has said he will come back on Monday to counter Musharraf's re-election bid and run for parliament, despite the threat of arrest.

An anti-terrorism court in the eastern city of Lahore on Friday ordered the arrest of Shahbaz Sharif in a murder case, said Aftab Ahmed Bajwa, a lawyer for the plaintiff.

He 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. Nawaz was Pakistan's prime minister.

On Wednesday, the father of one of the victims asked the court to arrest Shahbaz after hearing that he was due to return to Pakistan, Bajwa said. Shahbaz has denied the allegations.

Meanwhile, an anti-corruption court in Rawalpindi held a hearing in a case involving allegations that the Sharif family defaulted on a bank loan and owned property beyond their known sources of income, said Zulfiqar Ahmed Bhutta, a prosecutor for the state National Accountability Bureau.

The cases date back to 2001 and 2002. Hearings had been adjourned for years, but were reopened late last month following an application by the government.

Bhutta said the prosecution sought a hearing in the case on Monday — the Sharifs' planned date of return to Pakistan — but the judge on Friday adjourned the case until Sept. 13 to ensure the next hearing takes place after the Sharifs are inside the country. The brothers are currently in London.

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."

"They cannot face his return, so they are initiating false cases to deny him a political role," Iqbal told The Associated Press.

He said the Sharifs would defeat the cases in court.

Musharraf, a key U.S. ally in the war on terror whose popularity has shrunk since his failed attempt to fire the country's top judge earlier this year, has repeatedly said that 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, and there could be unrest. The Sharifs plan to continue to Lahore, the capital of Punjab and their power base, by road.

Iqbal said more than 1,300 workers 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.

A police official in Lahore acknowledged that officers had picked up Sharif supporters, but put their number at about 350. He spoke on condition of anonymity because he is not authorized to make media comments.

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 mid-September.

"The political process is moving forward. The government will not allow that political process to be disturbed," Durrani said.