British embassies around the world were today put on heightened security alert amid concerns of possible reprisal attacks by al-Qa’ida following the killing of Osama bin Laden.
Foreign Secretary William Hague said that elements of al-Qa’ida were still "in business" and they would need to be vigilant for "some time to come".
"This is not the end of being vigilant against al-Qa’ida and associated groups," he told the BBC Radio 4 Today programme.
"There may be parts of al-Qa’ida that will try to show that they are in business in the coming weeks, as indeed some of them are.
"So I have already this morning asked our embassies to review their security to make sure that vigilance is heightened and I think that will have to be our posture for some time to come."
Mr Hague added: "This is a very serious blow to al-Qa’ida but, like any organisation that has suffered a serious blow, they will want to show in some way that they are still able to operate."
The Foreign Secretary, visiting the Egyptian capital Cairo, said the "removal" of bin Laden was a "very, very positive development".
"It is unequivocally a good thing that he is no longer able to pursue terror, murder and mayhem in the world," he said.
But he stressed that it did not mean an end to the international military mission in Afghanistan, from where al-Qa’ida launched the 9/11 attacks in 2001.
"Just as we should be clear that this is an important and positive development, we should also be clear that the problems we are dealing with have not gone away," he said.
"We will still have to be vigilant, even more vigilant, in the coming days about the international terrorist threat.
"The work in Afghanistan will continue to be phenomenally difficult and must go on. So it would be wrong to draw the conclusion that suddenly we have solved a mass of the world's problems."
Mr Hague acknowledged that there had been a "general assumption" that bin Laden was hiding in the mountainous, tribal regions of Pakistan rather than the area around the capital, Islamabad.
But he added: "I don't think we're surprised by anything any more."
Former home secretary and defence secretary Lord Reid warned that there should not be the "least bit of complacency" following bin Laden's death.
"I would caution against premature celebration. Al-Qa’ida have lost a major, major figure but they are not finished. It is precisely at this time that our opponents are at their most dangerous," he told the Today programme.
David Blunkett, another former home secretary, added: "I think we are at more risk temporarily today than we were yesterday. We need to be extremely vigilant."
Defence Secretary Liam Fox said he had ordered all British military bases to maintain a "high level of vigilance" in the wake of bin Laden's death.
"In view of the possibility of violent attacks from al-Qa’ida or its sympathisers, I have directed my department to maintain a high level of vigilance in all UK defence facilities at home and abroad," he said.