Al-Qaeda declares death curse on US as they confirm Osama bin Laden death

In a statement dated Tuesday, Al-Qaeda confirmed that Bin Laden was dead, disappointing conspiracy theorists who refuse to believe he has been killed. Al-Qaeda has vowed to carry out revenge attacks on the US and its allies over the killing of Osama bin Laden, warning that celebrations in the west would be replaced by sorrow and blood.

The statement on a jihadist website was the first by al-Qaeda since Bin Laden's death, which it said would become "a curse that hunts the Americans and their collaborators, and chases them outside and inside their country".

The White House spokesman, Jay Carney, said they were aware of the statement and that US security, both at home and at embassies and bases overseas, has been on high alert since Sunday.

The Department of Homeland Security has warned US train operators to be especially careful after officials said that among computers, hard disks and other material taken from the Abbottabad compound they found a vague plan to attack the US rail network on this year's 10th anniversary of 9/11. One proposal was to demolish part of a rail track so that a train would fall into a river or valley, according to US officials.

The statement went on to say Bin Laden's death would not deflect al-Qaida from its war against the US and its allies, which include the Pakistani government. It called on Pakistan to rise up against the "traitors".

The discovery of Bin Laden's hide–away so close to the capital, Islamabad, has strained relations between the US and Pakistan. Carl Levin, chairman of the Senate armed services committee and a Democrat, ordered an investigation into whether the Pakistani government and intelligence services knew of his whereabouts. "We need these questions about whether or not the top level of the Pakistan government knew or was told by the ISI, their intelligence service, about anything about this suspicious activity for years in a very, very centralised place," Levin said.

The senator, who is usually guarded in his public statements, hinted that he believed some senior figures in Pakistani intelligence knew where Bin Laden was hiding – comments that will further inflame the Pakistani government.

"I think at high levels – high levels being the intelligence service – they knew it," Levin said. "I can't prove it. I just think it's counterintuitive not to."

He raised doubts about continuing the billions of dollars in aid to Pakistan, which requires congressional approval.

The Obama administration so far has been reluctant to criticise the Pakistani government and has opted instead to stress the positive aspects of the ties. The strategy seems to be to try to use Pakistan's embarrassment to prise out other al-Qaida or Taliban figures who may be living in Pakistan, such as the Taliban leader, Mullah Omar, and Bin Laden's deputy, Ayman al-Zawahiri.

United Nations human rights investigators have called on Washington to disclose whether there had been any plan to capture Bin Laden. While they acknowledged the difficulties involved in such terrorist-related missions, they raised questions about the legality of the killing.

Meanwhile the New York Times reported that the US may have targeted one of the men named as a possible successor to Bin Laden. Quoting American officials, the paper said a missile strike from an American military drone in a remote region of Yemen on Thursday was aimed at killing Anwar al-Awlaki, the radical American-born cleric believed to be hiding in the country.

Separately it was reported that a Saudi man accused of conspiring with Bin Laden in the bombings of two US embassies expects to be extradited in the next few months to face charges after more than 12 years in British custody, according to documents which have emerged from a US court.

Prosecutors in New York have charged Khalid al-Fawwaz with helping al-Qaida to orchestrate the 1998 car bombings of the US embassies in Kenya and Tanzania, which killed 224 people.