Michael Bloomberg, the mayor of New York, has said that the Boston Marathon bombing suspects intended to blow up their remaining explosives in Times Square.
Speaking at a joint press conference on Thursday with Police Commissioner Raymon Kelly, Bloomberg said that the Tsarnaev brothers had a pressure cooker bomb and five pipe bombs they intended to set off.
On Friday, authorities transferred surviving suspect Dzhokhar from the hospital to a federal detention centre outside of Boston.
"The surviving attacker revealed that New York City was next on their list of targets," Bloomberg said at New York City Hall.
"He and his older brother intended to drive to New York and detonate those explosives in Times Square."
The mayor said that Dzhokhar told Boston investigators from his hospital bed that he and his brother Tamerlan had discussed "spontaneously" going to New York to detonate their remaining explosives.
Miriam Conrad, Tsarnaev's lawyer, declined to comment on Thursday on whether her client was still talking with investigators.
On Wednesday, two US officials, speaking anonymously to the AP news agency, revealed that the federal government had added Tamerlan to a terrorist database 18 months before the deadly explosions.
Washington is attempting to piece together what happened and whether there were any unconnected dots buried in the US government files that, if connected, could have prevented the bombings.
"It's now clear that both the FBI and the CIA were aware of Tamerlan Tsarnaev for more than a year," said Al Jazeera reporter Dominic Kane.
"When the hunt for the Tsarnaev brothers concluded last week, police and law enforcement agencies spoke of it as a victory.
"But now the revelation that Tamerlan Tsarnaev was on a watchlist of potential terror suspects might put that in a different light."
Tsarnaev, 19, told authorities that his older brother, 26, had only recently recruited him to be part of the attack, the US officials said on Wednesday.
The teenager is said to have told the FBI that he and his brother were angry about the US wars in Afghanistan and Iraq and the killing of Muslims there, officials said. How much of those conversations will end up in court is unclear.
The CIA added Tamerlan to a huge, classified database of known and suspected terrorists a year and a half ago, officials said, an acknowledgment that will undoubtedly prompt a congressional inquiry about whether the Obama administration adequately investigated tips from Russia that Tsarnaev had posed a security threat.
Shortly after the bombings, US officials said the intelligence community had no information about threats to the marathon before the April 15 explosions.
The US officials who spoke to AP were close to the investigation, but insisted on anonymity because they were not authorised to discuss the case with reporters.
Investigators have said the brothers appeared to have been radicalised through materials on the internet and have found no evidence tying them to any one group.
Tamerlan, whom authorities have described as the driving force behind the plot, was killed in a shootout with police.
The CIA made the request to add Tamerlan's name to the terrorist database after the Russian government contacted the agency with concerns that he had become a follower of extremism.
About six months earlier, the FBI had separately investigated Tsarnaev, also at Russia's request, but the FBI found no ties to terrorism, officials said.
Officials say they never found the type of information on Tsarnaev that would have elevated his profile among counterterrorism investigators and placed him on the terrorist watch list.
Politicians who were briefed by the FBI said they had more questions than answers about the investigation of Tsarnaev.
The Senate is due to be briefed on the investigation on Thursday.
Dzhokhar reportedly acknowledged to the FBI his role in the attacks but did so before he was advised of his constitutional rights to remain silent and seek a lawyer.
|Bombings suspect Dzhokhar Tsarnaev was captured unarmed [AFP]
It is unclear whether those statements would be admissible in a criminal trial and, if not, whether prosecutors would need them to win a conviction.
Officials said physical evidence, including a 9mm handgun and pieces of a remote-control device commonly used in toys, was recovered from the scene.
Authorities had previously said that Dzhokhar exchanged gunfire with them for more than an hour on Friday night before they captured him inside a boat covered by a tarp in a suburban Boston neighbourhood backyard.
But the two US officials said on Wednesday that he was unarmed when captured, raising questions about the gunfire and how he was injured.