NEW YORK » The Boston Marathon bombers were headed for New York’s Times Square to blow up the rest of their explosives, authorities said today, in what they portrayed as a chilling, spur-of-the-moment scheme that fell apart when the brothers realized the car they had hijacked was low on gas.

"New York City was next on their list of targets," Mayor Michael Bloomberg said.

New York Police Commissioner Raymond Kelly said Dzhokhar Tsarnaev told interrogators from his hospital bed that he and his older brother decided on the spot last Thursday night to drive to New York and launch an attack. In their stolen SUV they had five pipe bombs and a pressure-cooker explosive like the ones that blew up at the marathon, Kelly said.

But when the Tsarnaev brothers stopped at a gas station on the outskirts of Boston, the carjacking victim they were holding hostage escaped and called police, Kelly said. Later that night, police intercepted the brothers in a blazing gunbattle that left 26-year-old Tamerlan Tsarnaev dead.

"We don’t know if we would have been able to stop the terrorists had they arrived here from Boston," the mayor said. "We’re just thankful that we didn’t have to find out that answer."

The news caused New Yorkers to shudder with the thought that the city may have narrowly escaped another terrorist attack, though whether the brothers could have made it to the city is an open question. They were two of the most-wanted men in the world, their faces splashed all over the Internet and TV in surveillance-camera images released by the FBI hours earlier.

Dzhokhar, 19, is charged with carrying out the Boston Marathon bombing April 15 that killed three people and wounded more than 260, and he could get the death penalty. Christina DiIorio-Sterling, a spokeswoman for U.S. Attorney Carmen Ortiz in Boston, would not comment on whether authorities plan to add charges based on the alleged plot to attack New York.

The Middlesex County district attorney’s office also is building a murder case against the surviving Tsarnaev for the death of MIT police officer Sean Collier three days after the bombings, office spokeswoman Stephanie Guyotte said.

Investigators and lawmakers briefed by the FBI have said the Tsarnaev brothers — ethnic Chechens from Russia who had lived in the U.S. for about a decade — were motivated by anger over the U.S. wars in Iraq and Afghanistan.

Based on the younger man’s interrogation and other evidence, authorities have said it appears so far that the brothers were radicalized via Islamic jihadi material on the Internet instead of any direct contact with terrorist organizations, but they warned that it is still not certain.

Dzhokhar was interrogated in his hospital room Sunday and Monday over a period of 16 hours without being read his rights to remain silent and have an attorney present. He immediately stopped talking after a magistrate judge and a representative from the U.S. Attorney’s office entered the room and gave him his Miranda warning, according to a U.S. law enforcement official and others briefed on the interrogation.

Kelly and the mayor said they were briefed on the New York plot on Wednesday night by the task force investigating the Boston bombing.

Rep. Peter King, R-N.Y., said in a CNN interview that the city should have been told earlier.

"Even though this may or may not have been spontaneous, for all we know there could be other conspirators out there, and the city should have been alerted so it could go into its defensive mode," he said.

Asked about the delay, Bloomberg said: "There’s no reason to think the FBI hides anything. The FBI does what they think is appropriate at the time, and you’ll have to ask them what they found and what the actual details of the interrogation were. We were not there."

Kelly, citing the interrogations, said that four days after the Boston bombing, the Tsarnaev brothers "planned to travel to Manhattan to detonate their remaining explosives in Times Square."

"They discussed this while driving around in a Mercedes SUV that they hijacked after they shot and killed the officer at MIT," the police commissioner said. "That plan, however, fell apart when they realized that the vehicle they hijacked was low on gas and ordered the driver to stop at a nearby gas station."

A day earlier, Kelly said that Dzhokhar Tsarnaev had talked about coming to New York "to party" after the attack and that there wasn’t evidence of a plot against the city. But Kelly said a later interview with the suspect turned up the information.

"He was a lot more lucid and gave more detail in the second interrogation," Kelly said.

Kelly said there was no evidence New York was still a target. But in a show of force, police cruisers with blinking red lights were lined up in the middle of Times Square on Thursday afternoon, and uniformed officers stood shoulder to shoulder.

"Why are they standing like that? This is supposed to make me feel safer?" asked Elisabeth Bennecib, a tourist and legal consultant from Toulouse, France. "It makes me feel more anxious, like something bad is about to happen."

Above the square, an electronic news ticker announced that the Boston Marathon suspects’ next target might have been Times Square.

Outside Penn Station, Wayne Harris, a schoolteacher from Queens, said: "We don’t know when a terrorist attack will happen next in New York, but it will happen. It didn’t happen this time, by the grace of God. God protected us this time."

In 2010, Times Square was targeted with a car bomb that never went off. Pakistani immigrant Faisal Shahzad had planted a bomb in an SUV, but street vendors noticed smoke and it was disabled. Shahzad was arrested as he tried to leave the country and was sentenced to life in prison.

With tens of millions of dollars in federal homeland security funding at stake, Bloomberg and Kelly have repeatedly sought to remind the public that New York remains at the top of terrorists’ wish list. They have said the city has been targeted in more than a dozen plots since 9/11.

Kelly said Dzhokhar was photographed in Times Square with friends in April 2012 and was in the city again in November 2012, but "we don’t know if those visits were related in any way to what he described as the brothers’ spontaneous decision to hit Times Square."

He said the police intelligence division is trying to establish Dzhokhar’s movements in the city and determine who might have been with him.

Meanwhile, the Tsarnaev brothers’ father said he is leaving Russia for the U.S. in the next day or two, but their mother said she was still thinking it over.

Anzor Tsarnaev has expressed a desire to go to the U.S. to find out what happened with his sons, defend the hospitalized son and, if possible, bring the older son’s body back to Russia for burial.

Their mother, Zubeidat Tsarnaeva, who was charged with shoplifting in the U.S. last summer, said she has been assured by lawyers that she would not be arrested, but was still deciding whether to go.

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Associated Press writers Verena Dobnik and Tom Hays in New York contributed to this story.