Al-Qaeda has confirmed the death of its leader, Osama Bin Laden, according to a statement attributed to the group and posted on jihadist internet forums.
The statement said his blood would not be "wasted" and al-Qaeda would continue to attack the US and its allies.
Bin Laden's death would be a "curse" for the US and urged an uprising in Pakistan, the statement added.
The militant was shot dead on Monday when US commandos stormed his compound in the Pakistani town of Abbottabad.
The covert raid was carried out without the prior knowledge of the Pakistani authorities, increasing tension between the two countries.
Several rallies were held in Pakistan on Friday in protest. The BBC's Syed Shoaib Hasan said thousands marched through central Karachi in the biggest such rally there in years. They chanted slogans praising Bin Laden - calling him a guardian of Islam.
The statement published on jihadist web forums, signed by "the general leadership" of al-Qaeda, said an audiotape would be released of Bin Laden speaking a week before his death.
"[His blood] will remain, with permission from Allah, the Almighty, a curse that chases the Americans and their agents, and goes after them inside and outside their countries," it warned.
"Their happiness will turn into sorrow, and their blood will be mixed with their tears. We call upon our Muslim people in Pakistan, on whose land Sheikh Osama was killed, to rise up and revolt.
"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."
Although US forces buried Bin Laden's body at sea, the statement warned the US that "multiple gates of evil" would be opened on them if they failed to hand over the corpse to his family. It incited Muslims to take action should the Americans mistreat the body or any of his captive family members.
It acknowledged the US was responsible for his death, and also noted that he had been killed by "treacherous infidel bullets".
The statement attracted a high number of online comments, all of which seemed to accept the death of Bin Laden as fact.
Correspondents say this contrasts starkly with the scepticism that followed President Obama's announcement on Monday of the al-Qaeda leader's death. The scepticism had led to calls for the US to release pictures of his corpse - a move resisted by President Obama.
White House spokesman Jay Carney said it was "aware" of the statement.
"What it does is acknowledge the obvious, which is that Osama Bin Laden was killed by US forces," he said.
"We are quite aware of the potential for [militant] activity and are highly vigilant on that matter for that reason."
The Afghan Taliban issued its own statement on Friday, saying the death of Bin Laden would give "new impetus to the current jihad".
"The sapling of jihad has always grown, blossomed and bore fruit through irrigation by pure blood," it added.
"The martyrdom of a martyr leads hundreds more to head to the field of martyrdom and sacrifice."
Earlier, Pakistani Islamist groups, led by the Jamaat-e-Islami, denounced the US military operation in Abbottabad as a violation of Pakistan's sovereignty.
They were also critical of Pakistan's government for allowing the commando operation to happen, although officials deny they were told.
Hundreds of people gathered in central Abbottabad following Friday prayers. They burned tyres, blocked a main road and shouted "down, down USA!" and "USA terrorist".
Our correspondent in Karachi said most groups taking part in rallies there were either banned by the Pakistani government or on a watch list for militant groups. Thousands took part but the rally remained largely peaceful, he adds.
Anti-American sentiment also appeared to be high at a similar protest in the south-western city of Quetta, the capital of Baluchistan province.
However, a BBC correspondent in Rawalpindi says the anti-US protest there was much smaller than expected with about 50 people turning up.
Meanwhile, reports from the US says documents found at the compound suggest Bin Laden was planning further attacks on the US, including on the 10th anniversary of 11 September 2001.
One plan was to target a US rail route, officials said, although no imminent threat was detected.
One of Bin Laden's wives being interrogated by Pakistani security officials said she had never left the upper floors of the compound the entire time she was there, believed to be about six years.
She and Bin Laden's other two wives were taken into custody following Monday's raid. Pakistani authorities are also holding eight or nine children who were found there.