Mayor Michael Bloomberg and police commissioner Raymond Kelly spoke at a briefing today.
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.
Mr Kelly had said a day earlier that the suspects were targeting New York, but was later briefed by federal officials.
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.
COMMENT RULES: Comments that are judged to be defamatory, abusive or in bad taste are not acceptable and contributors who consistently fall below certain criteria will be permanently blacklisted. The moderator will not enter into debate with individual contributors and the moderator’s decision is final. It is Belfast Telegraph policy to close comments on court cases, tribunals and active legal investigations. We may also close comments on articles which are being targeted for abuse. Problems with commenting? email@example.com