Police in the Brazilian city of Rio de Janeiro have launched a major operation to try to stop a wave of violence by criminal gangs.
For three days, suspected gang members have been blocking roads, burning cars and shooting at police stations.
Military police have been deployed in 17 different slum districts.
Rio's governor says the violence is retaliation by drugs gangs who have been driven out of some areas by a police pacification programme.
More than 1,000 officers had been taken away from desk jobs to join the surge on the streets, the military police said, and 300 extra motorcycle police were on patrol.
Rio de Janeiro's state governor Sergio Cabral has also asked the central government for police reinforcements from outside Rio to keep the main highways open.
Two suspected gang member have been shot dead.
More than eight others have been arrested, including four suspects who were found with petrol bombs in the Copacabana beach neighbourhood.
Starting on Saturday night, armed men have been blocking some of the main roads leading out of Rio, robbing motorists and setting their vehicles on fire.
The authorities are convinced that the attacks are being orchestrated by drugs gangs in retaliation for being forced out of their traditional strongholds in some slum districts by police pacification units.
"Without doubt these attacks are related to the reconquest of territory and the new policy of public security in Rio de Janeiro," Mr Cabral said.
"We are not going to retreat in this policy. We are going to push forward, pacifying communities and bringing peace to the population."
Rio's police have been taking back control of poor neighbourhoods, known as favelas, that have for years been controlled by heavily armed drug trafficking gangs.
The pacification programme is aimed at improving security and the rule of law in Rio, which will host the Fifa football World Cup in 2014 and the Olympic Games in 2016.
Military vehicles enter Brazil slum
Armoured carriers roll into Vila Cruzeiro slum in Rio de Janeiro as security forces prepare to take on drug gangs.
Military armoured vehicles have rolled into the Vila Cruzeiro slum in northern Rio de Janeiro in support of a police crackdown on Brazilian drug gangs.
Thursday's show of strength came after five days of unrest in the city, during which police stations were attacked and armed groups stopped vehicles, robbed the occupants and set fire to cars.
At least 23 people have been killed and 153 have been arrested as Brazilian security forces seek to crush the gangs and impose the law in the violent slums, known as favelas.
The crackdown has seen police deploying armoured personnel carriers, helicopters and thousands of heavily armed agents.
It is part of the government's wide-spread strategy to control crime in the favelas in the lead up to the country's hosting of the World Cup in 2014 and the Olympic Games in 2016.
Footage from Brazil's TV Globo showed heavily armed drug traffickers escaping to a neighbouring community on pick-up trucks and motorbikes, running through dirt roads on the top of hills.
But Lilia Teles, a TV Globo reporter, told Al Jazeera that that criminals are still setting fires to buses and cars in the city, and that shotgun blasts can be heard in Rio's streets.
Bloody clash anticipated
Al Jazeera's Gabriel Elizondo has been monitoring the situation from Sao Paulo, and said that the public hospital nearest to Vila Cruzeiro has been "urgently sending out messages for all of the trauma doctors to please come to the hospital immediately, because they're expecting that this could get very bloody".
He also reported that while police in Rio de Janeiro have been engaged in favela occupation programmes over the past two years, the situation in Vila Cruzeiro is unique.
"This is really a big deal ... this is the first time ever, in Brazil's history, in the history of Rio, that the civil police have ever used any sort of these armoured personnel carriers in an operation such as this."
Six of the armoured vehicles entered the Vila Cruzeiro favela, where police say the drug gangs have taken refuge after they were forced out of 13 other slums.
The gangs are fighting back by opening fire on police stations and setting cars and buses ablaze, police said.
Our correspondent said that the violence that rocked Rio de Janeiro in recent days is a clear message from the drug traffickers.
"This is basically them saying, 'We're still here, we still can wreak havoc, we can still cause panic in the city'" Elizondo said.
Rio favela violence: How police use hard and soft tactics
For many years the sight of police officers in one of Rio de Janeiro's most notorious favelas signalled to inhabitants that a shoot-out with members of a drug gang was most likely imminent.
Many favelas have long been controlled by heavily armed drugs gangs, which use the slums as a base from which to distribute supplies and impose their own arbitrary punishments on those who offend them or risk attracting police attention.
Police have been criticised by human rights groups for too often using lethal force without justification in Brazil's favelas and many of the poorest communities came to fear those who were meant to protect them.
The introduction of Police Pacification Units (UPPs) in Rio two years ago has seen the first sustained attempt to break this cycle, enforce the rule of law in favelas and win the hearts and minds of the next generation.
Sergio Cabral, the governor of Rio de Janeiro state, changed the city's approach to security issues after a visit to Colombia in 2007 during which he visited the cities of Bogota and Medellin, which have also been scarred by battles between drugs gangs and police.
After his return he secured $1.7 billion (£1.1 billion) of federal funding to develop favelas.
UPPs were subsequently launched alongside this programme, under the guidance of Jose Mariano Beltrame, the state's public security secretary.
The units are typically spearheaded by elite officers from the Special Police Operations Battalion (BOPE) but they also involve police showing a softer side by offering classes to children in day care centres.
In the City of God favela, which became known worldwide after the film of the same name, police act as teachers for everything from karate to music.
Police officers based in the units receive generous monthly bonuses.
The authorities hope that by 2014, when Brazil will host the World Cup for the first time since 1950, there should be at least 12,500 police working in 40 or more UPPs in Rio.
Only time will tell whether the violence of recent days has dealt a significant blow to that ambition.
And I decided to add pics and videos...
Literally hundreds of drug dealers were seen running away
And I guess I should add that Rio deserves better, that there's a lot more to Rio than these bloody stories and that "Rio de Janeiro remains beautiful" .
Pics taken from here and here.
Huge, huge operation. I'm not there but there seems to be a mix of frustration, hope, doubt, confidence, fear...