Police in the Pakistani city of Karachi used sticks to beat up protestors as lawyers began an anti-government protest march.
Organisers intend the four-day march to culminate in a sit-in at the parliament in the capital, Islamabad, on Monday.
The demonstrators want President Asif Ali Zardari to fulfil a pledge to reinstate judges sacked under former President General Pervez Musharraf.
The government says the march is aimed at destabilising the country.
Police have arrested more than 400 opposition activists in the past few days.
The authorities have also banned political gatherings in the country's two largest provinces, Punjab and Sindh, saying they could trigger bloodshed.