A suspected leading member of al-Qaeda has slipped back into Kenya, the authorities there believe.
An attack on a hotel near Mombasa last November killed 15
All UK flights to Kenya are being suspended in the wake of intelligence information that the threat level to British planes has increased to imminent.
These two developments show that the terror nightmare is back to haunt East Africa, if it ever went away.
Kenya in particular has suffered a number of attacks widely believed to have been carried out by groups linked to al-Qaeda.
These include the bombing of the American embassy in Nairobi in 1998, the 2002 attack on an Israeli-owned hotel in Mombasa last year and - on the same day - the attempted shooting down of an Israeli airliner.
The government in Kenya and neighbouring countries have made strenuous efforts in recent months to tighten security.
But they do not have a sophisticated security apparatus for dealing with attacks by groups like al-Qaeda and are vulnerable because of their long and porous borders.
On Wednesday, the Kenyan Government said it was stepping up security at vital installations, particularly those with American and British interests.
The government said this move was being taken because it had evidence that a terrorist attack was being planned in East Africa - most probably Kenya - before the end of the month.
Matthew Kabetu, head of Kenya's anti-terrorism unit, said that Fazul Abdullah Mohammed, suspected of involvement in the Nairobi and Dar es Salaam bombings and the attacks in Mombasa, may be back in the country.
The Kenyans' warnings prompted the United States to urge its citizens to postpone non-essential trips there.
This call has been echoed by the Foreign Office in London.
Tens of thousands of British people travel to Kenya every year and so the UK decision to suspend flights there is a severe blow to the tourist industry.
But it is also a blow to a country which knows first-hand the horror of terrorism.
Suspect Fazul Abdullah Mohammed is believed to be in Kenya or Somalia
Some 219 people were killed in the 1998 embassy bombing, blamed on Osama Bin Laden al-Qaeda's network.
There was a massive security operation involving the US Federal Bureau of Investigation to hunt down the perpetrators - 12 others were killed in a simultaneous attack in neighbouring Tanzania.
During the trial in the US of those charged with the bombing of the Nairobi embassy, a witness who admitted to being a former member of the al-Qaeda network said that two of the men eventually on trial were living in Kenya.
Last November, 15 people, mostly Kenyans, were killed in a suicide attack on the hotel near Mombasa - a cruel demonstration of the difficulty of ensuring security in holiday destinations that are soft targets for would-be attackers.
There is no doubt among Western intelligence agencies that groups linked to al-Qaeda are still active in East Africa.
But the security problems which Kenya faces are immense.
It has long, remote borders with Tanzania, Uganda, Sudan, Somalia and Ethiopia. These are hard to police for a country with limited financial and human resources to commit to border patrols.
The border with Somalia is particularly troublesome for the country and has for decades seen incursions into Kenya by armed bands known as shiftas.
They are frequently involved in smuggling anything from ivory to weapons.
In nearly 40 years of independence, Kenya has been unable to police this area effectively.
The 10 years of conflict and instability in Somalia have made weapons easily available in Somalia's border areas.
The US State Department in its country information on Kenya says that there are concerns about the wider links of Somali armed groups.
"There are indications of ties between Muslim extremist groups, including Osama Bin Laden's al-Qaeda organisation, and these roving groups of Somali gunmen," the document says.