Security has been tightened on Sao Paulo's streets

A police chief urged people to "go out and have fun" over the weekend as his officers kept watch on the streets.

Violence erupted last week with prison riots and attacks on police, organised by criminals based in Brazil's jails.

Officials deny the charge that a police crackdown, in which some 107 suspects reportedly died, was heavy-handed.

But human rights groups are demanding an investigation into the police response, amid allegations that many people in poorer neighbourhoods were the victims of extra-judicial killings.

Forty-one police officers and prison guards, 18 inmates and four civilians were also among those killed in the past week's violence, police say.

I say to our people, the police are still in the streets, they can go out and have fun this weekend Police Col Elizeu Eclair Brazil's mighty prison gangs

Motorists are being frisked at checkpoints across Sao Paulo and heavily armed police are patrolling neighbourhoods on foot.

Military police commander Col Elizeu Eclair said the emergency security measures could be kept in place for weeks.

But on Friday, after a night of relative calm in Sao Paulo, he said life was returning to normal.

"I say to our people, the police are still in the streets, they can go out and have fun this weekend," Col Eclair is quoted by the Reuters news agency as saying.

Political row

The BBC's Steve Kingstone in Sao Paulo says that if Col Eclair is proved right and the weekend is quiet, this may simply be because neither the police nor the crime gangs have any reason for prolonging the conflict.

He says the police have been criticised over their crackdown, while the criminals may use a lull to generate more funds through drug trafficking and racketeering.

The violence began on Friday last week, when police were attacked in apparent retaliation for the transfer of 765 jailed members of the First Command of the Capital (PCC) to a maximum-security prison.

A police union is suing security officials, saying they should have foreseen the violent consequences of the transfer.

Telecoms companies have meanwhile disabled mobile phone masts near six prisons around Sao Paulo state after reports that the PCC's jailed leaders used mobile phones to orchestrate the violence on the streets.

Our correspondent says a political row over the causes of the violence looks set to intensify as the clashes subside.

The past week has seen the state and federal governments and rival parties blaming each other for security failings.

Brazilian President Luiz Inacio Lula da Silva will face a former Sao Paulo governor in an election battle for the presidency this year, and crime is at the top of the agenda.