Al-Qaida conceded in an 11-paragraph statement Friday that its leader, Osama bin Laden, was dead, but also warned Western countries that attacks would be carried out on the United States and its allies in revenge.

The statement, published on a jihadist website, said Al-Qaida would soon release a taped message from bin Laden and said that his blood "is more precious to us and to every Muslim than to be wasted in vain."

Reuters reported:

Al Qaeda urged Pakistanis to rise up against their government to "cleanse" the country of what it called the shame brought on it by bin Laden's shooting and of the "filth of the Americans who spread corruption in it."

"Before the sheikh passed from this world and before he could share with the Islamic nation in its joys over its revolutions in the face of the oppressors, he recorded a voice recording of congratulations and advice which we will publish soon, God willing," the militant group said.

The statement also warned Americans not to harm bin Laden's corpse and to hand it and those of others killed to their families, although U.S. officials say bin Laden's body has been buried at sea and no other bodies were taken from the compound.

The statement also warned of retaliatory attacks to last Sunday's raid in Abbottabad.

"We will continue to hunt the Americans and their operatives inside and outside their country," the statement said. "Soon by God's help, their happiness will be turned to grief and their tears will be mixed with their blood."

Fears of an attack were heightened when intelligence analysts revealed that bin Laden may have been leading a plot to attack U.S. rail and subway systems on this year's 10th anniversary of the September 11th attacks. Since the raid, the United States has been on high alert.

From The Guardian:

The White House spokesman, Jay Carney, said of the al-Qaida statement: "We are aware of it. What it does, obviously, is acknowledge the obvious, which is that Osama bin Laden was killed on Sunday night by US forces.

"We're being extremely vigilant. We're quite aware of the potential for activity and are highly vigilant on that matter for that reason.

"US security, both at home and at embassies and bases overseas, has been on high alert since Sunday."

The department of homeland security (DHS) has warned US train operators to be especially careful after officials said that among computers, hard discs and other material taken from the Abbottabad compound they found a vague plan to attack the US rail network on the 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 White House spokesman said: "One of the things we saw, I think, was the notice that DHS put out with regard to the information collected about the consideration at least of a terrorist plot against American railways back in February of 2010. The fact that the world's most wanted terrorist might have been considering further terror plots against the United States is not a surprise, but it reminds us, of course, that we need to remain ever vigilant."