The Boston Marathon bombing suspects intended to blow up their remaining explosives in Times Square, New York City officials have said.
Mayor Michael Bloomberg and police commissioner Raymond Kelly spoke at a briefing where Mr Kelly said the two suspects had a pressure cooker bomb and five pipe bombs they wanted to set off.
They said Dzhokhar Tsarnaev told Boston investigators from his hospital bed that he and his brother had discussed going to New York to detonate their remaining explosives. They said they decided it spontaneously.
Tsarnaev travelled to New York at least once last autumn. There is a photo of the suspect in Times Square. Tsarnaev's older brother, Tamerlan, died in a shootout with police.
The plan fell apart after the Tsarnaev brothers were intercepted by police in a stolen car and got into a fierce gun battle that left Tamerlan Tsarnaev dead, Mr Kelly said.
Dzhokhar, 19, is charged with carrying out the April 15 bombing that killed three people and wounded more than 260, and he could get the death penalty.
He was interrogated in his hospital room over a period of 16 hours without being read his constitutional rights. He immediately stopped talking after a magistrate judge and a representative from the US Attorney's office entered the room and read him his rights, according to a US law enforcement official and others briefed on the interrogation.
The developments in New York came as federal authorities in Washington were piecing together the case and whether there were any unconnected dots buried in US government files that, if connected, could have prevented the attacks.
The federal government added Tamerlan's name to a terrorist database 18 months before the attacks, US officials told the Associated Press. Dzhokhar Tsarnaev told authorities that his older brother only recently recruited him to be part of the attack, two US officials said.
Investigators have said the brothers, Russian-born ethnic Chechens, appeared to have been radicalised through jihadist materials on the internet and have found no evidence tying them to a terrorist group.