Followers of Osama bin Laden have called for revenge against the United States just hours after President Barack Obama announced the terrorist leader had been killed.

On extremist websites people prayed that the al-Qaida leader was still alive and said his message of jihad would "never die".

Alluding to retribution for his death, one person added: "Brothers and sisters, wait and see, his death will be a blessing in disguise."

On another Arabic forum one writer posted: "Oh God, please make this news not true...God curse you Obama."

The writer added: "Oh Americans...it is still legal for us to cut your necks."

Britain’s Foreign Secretary William Hague said he had told embassies around the world to be on high alert following the news.