(CNN) Pakistani police Wednesday used tear gas on a group of journalists and supporters gathered outside parliament for a demonstration organized by former Pakistani Prime Minister Benazir Bhutto, police sources told CNN. Hundreds of people took part in the demonstration, and many remain outside parliament, the sources said.
Video showed Pakistani forces in uniform with shields and sticks trying to move a razor wire barricade surrounding the protesters.
Other police fired tear gas canisters into the air.
Some of the demonstrators clapped and and chanted slogans, while others raised their Bhutto posters into the air. Journalists aimed their cameras toward the line of police, who protected themselves with their shields as several protesters pushed the razor wire toward them.
Before the clashes began, Bhutto said 400 members of her political party were arrested across Pakistan on Wednesday "without any provocation."
At a news conference, Bhutto called on the people of Pakistan to join protests against President Gen. Pervez Musharraf's statewide emergency rule and his suspension of the country's constitution. Watch Bhutto talk about the crisis "
Bhutto also is calling for a massive rally on Friday, but a spokesman for Musharraf's government warned that such a demonstration is outlawed under the emergency measures.
Authorities in Punjab province have already barred a rally by Bhutto's Pakistan People's Party. A spokesman for the government said that large public gatherings are "generally inadvisable and the political parties should refrain from holding public meetings and rallies."
Government officials insist the declaration was necessary to the country's fight against terrorism and would not derail its slow progress toward democracy.
Opposition leaders, however -- and fired Supreme Court Chief Justice Iftikhar Muhammed Chaudhry -- accuse Musharraf's government of moving to shut down the judiciary just before the Supreme Court was to rule on a challenge to his election to a third term as president.
In an editorial published Wednesday in the New York Times, Bhutto said "the United States can promote democracy...by telling General Musharraf that it does not accept martial law, and that it expects him to conduct free, fair, impartial and internationally monitored elections within 60 days under a reconstituted election commission."
The United States, Britain and other countries have urged Musharraf to lift the emergency declaration and return to a constitutional government. While the United States and Britain have said they are reviewing current aid packages with an eye toward possible withdrawal, only the Netherlands has cut off financial aid to Pakistan.
Bhutto, who is seeking the prime minister's post in parliamentary elections that had been scheduled for January, said she is no longer talking with Musharraf about any kind of power-sharing deal. But officials from her party said advisors for the two are in touch.
Musharraf, who is the Pakistani army's chief of staff as well as the country's president, had promised to relinquish his ties to the military before Nov. 15, when he is expected to take the oath of office for a third five-year term.