Brazilian security forces have moved into a major Rio de Janeiro slum, after warning drug traffickers to surrender or face an assault.
Exchanges of fire were heard near the Alemao favela, where hundreds of alleged drug traffickers are believed to be hiding.
Some 2,600 police and troops, backed by armoured vehicles and helicopters, are taking part in the operation.
Within hours of moving in, police said they had taken control of the favela. 'We won. We brought freedom to the residents of Alemao,' said the head of Rio's military police, Mario Sergio Duarte.
But other officers have said they had not taken over all of the complex, and gunfire is still being heard in the area.
Dozens of people have been killed since the offensive began a week ago.
Brazilian authorities say the operation aims to make the city safer ahead of the World Cup in 2014 and Olympic Games in 2016.
Paratroopers, marines and members of elite police units began to enter favela da Grota, part of the larger Alemao complex of slums in northern Rio, early yesterday.
'We're entering the complex by four points. Alemao is surrounded and other troops are entering by other areas,' the civil police chief, Allan Turnowski, told Brazil's Globo TV earlier.
'A helicopter is involved in the offensive and another is filming the action, pointing out where drug traffickers are hiding. The majority are already hiding inside their houses,' Mr Turnowski added.
A deadline given to drug gangs to give themselves up ran out at sunset last Saturday, and police warned they would use violence if necessary.
Reports suggest that only 30 of about 500 to 600 drug traffickers in the area surrendered before the deadline.
The BBC's correspondent in Rio says flushing out the heavily armed drug dealers is a complex task in a densely populated area, but that so far they have encountered less resistance than expected.
But, our correspondent says, if the authorities are winning this battle against the drug lords, they have yet to win the war. — heavy-handed.