Pakistani police officers stand guard outside the apartment of Javed Hashmi, acting president of Pakistan Muslim League-N, 22 Sep 2007

Government officials say the arrests were to prevent ongoing public protests against Mr. Musharraf's government from getting out of hand.

But opposition parties say the 30-day detentions are clearly aimed at silencing critics of Mr. Musharraf's bid for re-election October sixth.

"This is a sham democracy. We condemn it. And, we will go to the courts. We will protest on this," said Ahsan Iqbal, the spokesman for the Pakistan Muslim League-Nawaz, one of the parties whose leaders were arrested late Saturday. "And, we want the world also to see what kind of democracy General Musharraf is running in Pakistan."

Opposition parties are petitioning Pakistan's Supreme Court to declare Mr. Musharraf's re-election bid unconstitutional, primarily because he is still head of the armed forces.

General Musharraf came to power in a peaceful military coup in 1999. He has been elected president once since then.