The government is trying to keep a lid on hardline anger
The latest deaths occurred when police opened fire on a crowd of several hundred people who had stormed a police station in the town of Kuchlak, near Quetta.
There was also a large demonstration in the southern city of Karachi, as well as smaller protests in the capital Islamabad and north-western Peshawar.
About 5,000 demonstrators took to the streets of Karachi chanting anti-US slogans, but there was no violence.
Reports say about 1,500 students marched in Islamabad, and several hundred turned out in Peshawar near the border with Afghanistan.
The deaths in Quetta came as Pakistan arrested three prominent Islamic leaders allied to Afghanistan's Taleban movement.
A 12-year-old boy was among those killed.
One man died and several were injured in the city of Quetta on Monday in a violent demonstration against the attacks on Afghanistan.
Planes heard
There were scenes of anger and grief from the family of the dead boy when his body was taken to the main hospital in Quetta.
As doctors worked fruitlessly to save the young boy's life, war planes could be heard overhead - the first daylight raids of the American and British campaign.
The BBC's Daniel Lak says mainstream Pakistani opinion does not support the anti-US rioters, or the Taleban.
But he says news of civilian casualties trickling out of Kabul will cause more widespread anger against the American and British raids.
Taleban sympathisers
With unrest continuing, the authorities detained Maulana Azam Tariq, head of the Sunni Muslim militant group Sipah-e-Sahabah Pakistan, at Lahore airport on Monday and placed him under house arrest in Punjab province, a party official said.
Earlier, two faction leaders of the Jamiat-e-Ulema Islam (JUI) party, Maulana Fazlur Rehman and Maulana Samiul Haq, were also placed under house arrest.
The men's parties are all members of the Afghanistan and Pakistan Defence Council, a pro-Taleban group of 35 parties which have pledged to resist the US-led attacks.
Pakistani Shia Muslims accuse Mr Tariq's party of mounting violent sectarian attacks on their community.
Mr Haq is believed to have been planning a meeting of the Afghanistan and Pakistan Defence Council to co-ordinate new protest action.
Mr Rehman's party for its part has promised fresh protests to demand his release.
The two men's JUI party has played a major role in demonstrations nationwide against the US-led action.
Flights suspended
Pakistan's state airline has indefinitely suspended flights to Quetta and other airports affected by violence whilst some foreign airlines have suspended flights to Pakistan altogether.
President Pervez Musharraf tried to calm the anger at the US-led attacks by telling his people that the action would be short and would cause few civilian casualties.
He said "the vast majority" of Pakistanis favoured his support for Washington whilst Islamabad had done everything possible to reach a negotiated solution to the crisis.