The so-called Pakistani Taliban has claimed responsibility for a failed car bombing in New York's Times Square - a claim city officials have denied.
A statement posted on the internet on Sunday said the attempted attack the previous day was to avenge the killing of two "Muslim martyrs", leaders of al-Qaeda linked groups in Iraq.
"The Pakistani Taliban announced its responsibility for the New York attack in revenge for the two leaders al-Baghdadi and al-Mahajer and Muslim martyrs," the statement read.
It referred to Abu Ayub al-Masri, also known as al-Mahajer, the head of al-Qaeda in Iraq, and Abu Omar al-Baghdadi, the purported head of the Islamic State of Iraq (ISI), an al-Qaeda affiliate.
The two were reportedly killed in a joint raid by US and Iraqi soldiers on April 18.
It was not immediately possible to verify the authenticity of the claim by a group which is largely responsible for domestic attacks targeting Pakistani military or government officials.
But Raymond Kelly, New York City's police commissioner, said there was no evidence to suggest the Pakistani Taliban was behind the incident.
"The intent of whoever did this [was] to cause mayhem [and] create casualties," he said.
'Extremely serious' incident
The White House described the incident as "extremely serious" and said it was looking into all possible motives behind the attempted attack.
Robert Gibbs, the White House spokesman, said Barack Obama, the US president, spoke to the city's mayor about the incident and will speak publicly on the issue later on Sunday.
"For the US, it's always safe and good for their own political advantage to accuse the Islamic militants even if it turned out that they have nothing to do with it"
New York authorities defused an explosive device discovered in a four-wheel-drive vehicle on Saturday evening, prompting the evacuation of thousands of people from the Times Square area of the city.
The police commissioner said a white man in his 40s had been identified on video footage of the area and was seen removing a dark shirt to reveal a red shirt about half a block from the vehicle.
Police said the device consisted of propane tanks, fireworks, petrol containers, wires and two clocks.
"We are treating it as if it could be a potential terrorist attack," Janet Napolitano, the homeland security secretary, said on Sunday morning.
Bomb-squad staff were deployed in the busy square in the heart of Manhattan after a T-shirt vendor, who saw smoke emerging from the car, alerted police.
Although the device had apparently started to detonate, there was no explosion, and authorities were on Sunday reviewing surveillance tapes and forensic evidence as they hunted for the driver of the vehicle.
The car was towed by police to a forensic facility in Jamaica, Queens, where investigators were looking for fingerprints and other DNA evidence.
'Terrorists around the world'
Michael Bloomberg, the New York's mayor, blamed the incident on "terrorists around the world", who want to take "freedoms" away from Americans.
But analysts told Al Jazeera that it was too early to blame the attempted attack on international "terrorists".
Mayor Bloomberg told the press: "We avoided what could have been a very deadly event"
Riad Kahwaji, a security analyst from the Institute for Near East and Gulf Military Analysis in Dubai, said it would be "premature to jump to conclusions".
"We have a precedent here, back in the 1990s, of the attack on the FBI building in Oklahoma city," he told Al Jazeera.
"People immediately accused Islamic militants and it turned out [the culprit] was one of the right-wing fundamentalists from inside the US.
"Right now, the big bogeyman is al-Qaeda, the Islamic terrorists. ... For the US, it's always safe and good for their own political advantage to accuse the Islamic militants even if it turned out that they have nothing to do with it."
Phil Rees, the author of Dining with Terrorists, also dismissed Bloomberg's comments about "terrorists" targeting American freedoms.
"I've spoken to Islamists for 20 years. They don't give a jot about my lifestyle in the United Kingdom or what goes on in America," he told Al Jazeera.
"They care about American foreign policy, what the United States is doing in Muslim lands, not just in Iraq and Afghanistan, but the way it has corrupted many Muslim leaders, the way that it prevents democracy emerging in Muslim lands, the way that it obviously doesn't look at Palestine and Israel in equal terms."