The two suspects in the Boston Marathon bombings intended to attack New York City next, Mayor Michael Bloomberg said Thursday.

"Last night, we were informed by the FBI that the surviving attacker revealed that New York City was next on their list of targets," he said at a news conference.

Police Commmissioner Ray Kelly said Dzhokhar Tsarnaev, the surviving suspect, discussed exploding bombs in Times Square with his brother Tamerlan, who was later killed in Boston in an exchange of gunfire with police.

Kelly says the two suspects had a pressure cooker bomb and five pipe bombs they wanted to set off.

Dzhokhar told investigators in the Boston hospital where he is recovering from his wounds about the plan, which Bloomberg said was spontaneous.

Tsarnaev travelled to New York at least once last fall. There is a photo of the suspect in Times Square.

Tsarnaev silent after Miranda warning

Sixteen hours after investigators began interrogating him, Tsarnaev went silent, after being read his constitutional rights.

Tsarnaev immediately stopped talking after a magistrate judge and a representative from the U.S. Attorney's Office entered his hospital room and gave him his Miranda warning, according to four officials of both political parties briefed on the interrogation. They insisted on anonymity because the briefing was private.

Before being advised of his rights, the 19-year-old suspect told authorities that his older brother, Tamerlan Tsarnaev, 26, only recently had recruited him to be part of the attack that detonated pressure-cooker bombs at the marathon finish line, two U.S. officials said.

Miranda warning Miranda rights, familiar to Canadians from U.S. crime dramas, guarantee the right to remain silent to avoid self-incrimination and the right to an attorney. Authorities can invoke a temporary public safety exception when they feel the public may be in immediate danger.

The CIA, however, had named Tamerlan to a terrorist database 18 months ago, said officials close to the investigation who spoke to The Associated Press on condition of anonymity because they were not authorized to discuss the case with reporters.

The new disclosure that Tamerlan Tsarnaev was included within a huge, classified database of known and suspected terrorists before the attacks was expected to drive congressional inquiries in coming weeks about whether the Obama administration adequately investigated tips from Russia that Tsarnaev had posed a security threat.

Shortly after the bombings, U.S. officials said the intelligence community had no information about threats to the marathon before the April 15 explosions that killed three people and injured more than 260.

The older Tsarnaev brother died Friday in a police shootout hours before Dzhokhar was discovered hiding in a boat in a suburban backyard. He was wounded.

Washington is piecing together what happened and whether there were any unconnected dots buried in U.S. government files that, if connected, could have prevented the bombings.

Lawmakers who were briefed by the FBI said they have more questions than answers about the investigation of Tamerlan Tsarnaev. House judiciary chairman Bob Goodlatte, a Republican from Virginia, said lawmakers intend to pursue whether there was a breakdown in information-sharing, though Representative Adam Schiff, a California Democrat who sits on the House intelligence committee, said he "hasn't seen any red flags thus far."

Senate to be briefed today

U.S. officials were expected to brief the Senate on the investigation today. The suspects' parents, Anzor Tsarnaev and Zubeidat Tsarnaeva, also plan to fly to the U.S. from Russia, the father was quoted as telling the Russian state news agency RIA Novosti. The family has said it wants to take Tamerlan's body back to Russia.

Rob (right) and Andrew, brothers of slain MIT police officer Sean Collier, react at his memorial service in Cambridge, Mass., on Wednesday. Thousands of law enforcement agents attended the memorial. (Brian Snyder/Reuters)

It is unclear whether the issue of their younger son's constitutional rights will matter since the FBI say he confessed to a witness. U.S. officials also said Wednesday that physical evidence, including a 9-mm handgun and pieces of a remote-control device commonly used in toys, was recovered from the bombing scene.

But the debate over whether suspected terrorists should be read their Miranda rights has become a major sticking point in the debate over how best to fight terrorism. Many Republicans, in particular, believe Miranda warnings are designed to build court cases, and only hinder intelligence gathering.

Christina DiIorio Sterling, a spokeswoman for U.S. Attorney Carmen Ortiz, said in an email late Wednesday, "This remains an ongoing investigation and we don't have any further comment."

Investigators have said the brothers appeared to have been radicalized through jihadist materials on the internet and have found no evidence tying them to a terrorist group.

U.S. investigators travelled to the predominantly Muslim province of Dagestan in Russia and were in contact with the brothers' parents, hoping to gain more information.

They are looking into whether Tamerlan, who spent six months in Russia's turbulent Caucasus region in 2012, was influenced by the religious extremists who have waged an insurgency against Russian forces in the area for years. The brothers have roots in Dagestan and neighbouring Chechnya but had lived in the U.S. for about a decade.

Investigators work around the boat where Dzhokhar Tsarnaev was found hiding. Conflicting reports cast doubt on whether he had a weapon when captured. (Darren McCollester/Getty Images)

Dzhokhar told the FBI that they were angry about the U.S. wars in Afghanistan and Iraq and the killing of Muslims there, officials said.

Dzhokhar's public defender had no comment on the matter Wednesday. His father has called him a "true angel," and an aunt has insisted he's not guilty.

Investigators have found pieces of remote-control equipment among the debris and were analyzing them, officials said. One official described the detonator as "close-controlled," meaning it had to be triggered within several blocks of the bombs.

That evidence could be key to the court case. And an FBI affidavit said one of the brothers told a carjacking victim during their getaway attempt, "Did you hear about the Boston explosion? I did that."

Officials also recovered a 9-mm handgun believed to have been used by Tamerlan from the site of an April 18 gun battle that injured a Massachusetts Bay Transportation Authority officer, two U.S. officials said.

No gun found in boat

The officials told the AP that no gun was found in the boat where Dzhokhar was hiding. Boston police Commissioner Ed Davis said earlier that shots were fired from inside the boat.

Asked whether the suspect had a gun in the boat, Davis said, "I'm not going to talk about that."

But Kurt Schwartz, director of the Massachusetts Emergency Management Agency, said a police officer was shot within a kilometre of where Tsarnaev was captured, "and I know who shot him."

Authorities had previously said Dzhokhar exchanged gunfire with them for more than an hour Friday night before they captured him inside a tarp-covered boat in a suburban Boston neighbourhood backyard. But two U.S. officials said Wednesday that he was unarmed when captured, raising questions about the gunfire and how he was injured.

In other developments: