WATERTOWN, Massachusetts (Reuters) - Gunfire was heard on Friday night as dozens of police cars and armored vehicles converged on a street in a Boston suburb in the manhunt for the surviving suspect in the Boston Marathon bombings, witnesses said.
A local CBS TV station cited Boston's mayor as saying a man believed to be the suspect was surrounded in Watertown. Reuters could not independently confirm that report.
An ethnic Chechen suspected in the Boston bombings is the target of a day-long manhunt that virtually shut down the city.
Shortly after police told a news conference the suspect was still on the loose, a Reuters witness saw dozens of police and armored vehicles rush to the street and then gunfire was heard.
"There's about 50 guys there with machine guns and they all got bulletproof vests on, some of them are holding shields and they're all congregated on the far end of Franklin Street," said another witness, Anna Bedirian, a resident of Franklin Street in Watertown. "There are a couple armored cars and they're all standing around."
Officials identified the fugitive as Dzhokhar Tsarnaev, 19, whose older brother, Tamerlan Tsarnaev, 26, whom the FBI also identified on Thursday as being involved in Monday's bombings, was shot to death overnight by police in a shootout. The surviving suspect escaped on foot.
Earlier on Friday, Colonel Timothy Alben told the news conference: "We do not have an apprehension of our suspect this afternoon. We remain committed to this."
Alben said officers went door-to-door in Watertown and searched houses. Officials followed a number of leads that were not fruitful and there was "much work to be done" he said.
Authorities cordoned off a section of Watertown and told residents not to leave their homes or answer the door as officers in combat gear scoured a 20-block area. Two Black Hawk helicopters circled the area. SWAT teams moved through in formation, leaving an officer behind to ensure that searched homes remained secure, a law enforcement official said.
The normally traffic-clogged streets of Boston were empty on Friday as the city went into lockdown after a bloody night of shooting and explosions. Public transportation had been suspended and air space restricted. Famous universities, including Harvard and MIT, closed after police ordered residents to remain at home.
Massachusetts Governor Deval Patrick said the "stay-in-place" order for Boston had been lifted and mass transit reopened as police pressed their search for Tsarnaev.
Monday's bombing on the finish line of the world-famous Boston Marathon, which killed three people and injured 176, was described by President Barack Obama as "an act of terrorism." It was the worst such attack on U.S. soil since the plane hijackings of September 11, 2001.
U.S. government suspects said the men had not previously been on the radar as possible militants.
Details emerged on Friday about the brothers, including their origins in the predominantly Muslim regions of Russia's Caucasus, which have experienced two decades of violence since the fall of the Soviet Union.
The fugitive described himself on a social network as a minority from a region that includes Chechnya, Dagestan and Ingushetia.
A man who told reporters he was an uncle of the brothers said they came to the United States in the early 2000s and settled in the Cambridge, Massachusetts, area.
Ruslan Tsarni, who lives in suburban Washington and said he had not spoken to the brothers since 2009, said the bombings "put a shame on our family. It put a shame on the entire Chechen ethnicity.
In separate interviews, the parents of the Tsarnaev brothers said they believed their sons were incapable of carrying out the bombings. Others remembered the brothers as friendly and respectful youths who never stood out or caused alarm.
"Somebody clearly framed them. I don't know who exactly framed them, but they did. They framed them. And they were so cowardly that they shot the boy dead," father Anzor Tsarnaev said in an interview with Reuters in Dagestan's provincial capital, Makhachkala, clasping his head in despair.
The FBI said the twin blasts were caused by bombs in pressure cookers and carried in backpacks that were left near the marathon finish line as thousands of spectators gathered.
The mother, Zubeidat Tsaraeva, speaking in English, told CNN, "It's impossible, impossible, for both of them to do such things, so I am really, really, really telling that this is a setup."
Additional reporting by Mark Hosenball, Alex Dobuzinskis, Aaron Pressman, Daniel Lovering, Ben Berkowitz, Emily Flitter and Jim Bourg; Writing by Grant McCool; Editing by Peter Cooney