A few months ago the story about al-Qaida was how, under pressure in Afghanistan and Pakistan, it had largely been unravelled and its operational abilities degraded. Now, after the attempted downing of a US jet bound for Detroit, the same sources – the US and UK intelligence agencies – say not only that al-Qaida is still a dangerous threat, but that it may have managed to export and reconstitute parts of its operations to Somalia and Yemen.

So what, precisely, should we believe? The reality is that there have always been Islamist groups in Africa who have described themselves as being al-Qaida. While some have been more closely associated with the core of Osama bin Laden's ideology and were involved in early al-Qaida spectaculars in Africa, others have used the name as a cover for criminality.

In the past two years, however, there have been a number of significant changes in Somalia and Yemen that have contributed to the emergence of a more widespread and cohesive jihadi ideology far more closely aligned to al- Qaida's aims and agendas.

In large part – at least in Somalia – US intervention has been responsible for the radicalisation. When the Islamic Courts Union emerged in Somalia in 2006 and brought a brief period of relative calm to the country it was America that encouraged its toppling. The consequence was a splitting away of a hardline faction of the courts' militia – known as the Shabaab – who the US defined as al-Qaida allies or proxies and have targeted, including with drones.

The emergence of the Shabaab, which controls large swaths of Somalia, has coincided – if the claims of the US intelligence agencies are to be believed – with events in the "Af-Pak" theatre. Seasoned Arab al-Qaida fighters have been replaced by Central Asians and transferred to Yemen and Somalia under the guidance of its chief of external operations, Saleh al-Somali, who was killed in a drone attack in Waziristan this month.

What has also been well documented in the past few months has been the existence of an active recruitment system targeting young Somalis with US, European and Australian passports to train in camps that have sprung up in Somalia in particular. Twenty, it is believed, travelled from Minneapolis alone. Twenty more from Stockholm are also thought to have attended training camps, along with dozens of young British Somalis. Last spring it emerged that some of the four Australian citizens arrested and charged with planning to attack an army barracks had trained in Somalia.

It is not only in Somalia that it is claimed al-Qaida is reconstituting itself. In Yemen an insurgency in the remote Shabwa region backed by groups claiming loyalty to al-Qaida has provided a second regional centre. It was there, four days ago, that an al-Qaida-supporting group said it had declared war on the US.

Large questions remain. A number of those who have gone back to fight – or be recruited for training – appear to have died fighting, particularly in Somalia. And while more than $1bn a year in remittances goes back to Somalia, suggesting that the Shabaab would not be short of money for operations, it is unclear how well al-Qaida operations in both Yemen and Somalia are organised.

Equally uncertain is the scope of their agenda: whether they are more focused for now on a local, rather than international, jihad. One thing, however, is quite clear. It is that the new al-Qaida has a very different face and a different base. If the threat is as real as suggested by the attempted attack on Northwest Airlines, the West's security services will be playing catch-up.