Pakistani police have blocked off the home of former prime minister Benazir Bhutto and served her with a three-day detention notice.
Ms Bhutto has vowed to wage a campaign to force President Pervez Musharraf to stand down as army chief.
The politician made an attempt to leave her house in Islamabad, but was blocked by police, who say that she is being detained for her own safety.
Police clashed with a number of Ms Bhutto's supporters, who attempted to stage protests around the country.
The BBC's Chris Morris says that more protests are likely as Gen Musharraf tries to consolidate the state of emergency he declared last Saturday.