ASHA HAD been raped by three men. The 13-year-old girl from the Somali port city of Kismayo was taken to the police station by her aunt to report the crime. Asha was the one who was arrested. After being held for three days and tried in secret by an Islamic court, Asha was sentenced to be stoned to death for adultery.

Kismayo's rulers encouraged people to come to the football stadium to watch the execution. A lorry load of stones was laid out. Asha, dragged kicking and screaming into the stadium, was buried in the ground. With around 1000 people watching, 50 men stepped forward and started hurling the stones at Asha's head. After a few moments, the stoning was stopped.

Two nurses were asked to step forward and check if she was still alive. She was, they said, so the stoning continued. Somalia has witnessed some brutal scenes in recent years. Ethiopian forces have been accused of assassinating civilians, firing indiscriminately at market crowds, and bombing residential areas. Somali government forces have deliberately killed journalists and human rights workers. All of the armed groups in Somalia have blood on their hands. But Asha's killing has served to highlight the growing power of a hardline Islamist group which analysts believe has links - or wants to have links - with al Qaeda.

Militia aligned to al Shabaab, a group that the US has designated a terrorist organisation, have been picking up territory in southern Somalia with ease. Merka, a small but strategic city 60 miles south of Mogadishu fell early this week. A far smaller town just 11 miles southwest of the capital fell on Thursday. In both cases, government-aligned forces fled without putting up a fight. The territories were claimed without a single bullet being fired.

Large swathes of central and southern Somalia are now under their control and there are rumours that Mogadishu may be next. The capital is supposedly controlled by Ethiopian and Somali government forces - but their control only really extends to the port, the airport and the presidential villa.

al Shabaab fighters are said to be free to move about Mogadishu with relative ease.

On paper it looks like a very similar situation to that in 2006 when the Islamic Courts Union (ICU) controlled most of the country. Their rule came to an end in Christmas 2006 when Ethiopian troops, with the tacit approval of the US, entered Somalia and drove the courts out. US assistant secretary of state Jendayi Frazer had warned that the ICU was ruled by "East Africa al Qaeda cell individuals", laying the philosophical groundwork for the Ethiopian intervention.

But few Somalis or independent analysts shared that belief. Instead they saw a relatively moderate Islamic authority which managed to do what no other group had done in nearly two decades - bring a semblance of law and order to the streets of Mogadishu.

It is something that the Somali government, backed by the UN and funded by Western donors, including Britain, has conspicuously failed to do. Instead, human rights groups have accused the Somali government and its Ethiopian allies of committing a succession of war crimes.

A series of bombings by the US, supposedly aimed at men they believe are terrorists, has served only to harden anti-American sentiment.

More than a million people have fled their homes, creating one of the world's gravest humanitarian catastrophes. Around half the population - some 3.2 million people - are now believed to be in need of emergency humanitarian assistance. But the level of violence, which includes the deliberate killing and targeting of aid workers, means that most of these people are out of the reach of aid agencies.

Into the vacuum has stepped a new generation of Islamist leaders who appear to fit Frazer's description a little better. They are, as one Somali analyst in Nairobi described them, "international jihadis".

Their links to al Qaeda are unproven but their ability to carry out well co-ordinated and targeted attacks was established last month when five bombs went off simultaneously in the northern cities of Hargeisa and Bosasso.

Hargeisa, the capital of Somaliland, a province in the north which has claimed independence, has always been seen as relatively safe. International aid agencies and the UN use it as a base for many of their activities elsewhere in the country. The attacks, aimed directly at international organisations including the UN, were designed to show that nowhere in Somalia is out of reach of the Shabaab.

As al Shabaab begins to take over, the Islamist leaders which Frazer dismissed as al Qaeda are now being actively courted by the international community. The softly spoken Sheikh Sharif Sheikh Ahmed is now based in Djibouti and is taking part in the UN's stuttering peace process. His office is funded by Western donors.

Sheikh Hassan Aweys, the more hardline ICU leader, is based in Eritrea and has been openly critical of the peace process. But Western diplomats, including officials from the US, have met with him and they hope to bring him on board.

The problem now is that these men, who once held Mogadishu and commanded the respect of all the Islamist militias, have been sidelined by more extremist leaders.