Major Ba-Hoku Barigye, Amisom's spokesman in Mogadishu, has daily contact with al-Shabaab. His phone beeps and rings every few seconds, day in, day out, as hundreds of texts and calls come in. Although they attempt to be blood-curdling, including repeated (and unfulfilled) threats to kill him, most are moronic, some unintentionally hilarious. "You are infidels and hypocrites the doomsday you are and your friend allah will punish as hell amisom i,m muslim and my religon is the best religon?" reads one.

Al-Shabaab controls much of southern Somalia and a good deal of Mogadishu. As an example of its concern for the wellbeing of ordinary Somalis, it recently forced the World Food Programme to suspend its activities in most parts of the south and said foreign humanitarian organisations were no longer welcome. Forty-seven aid workers, most of them Somali, were killed in 2009 and many were abducted. Al-Shabaab doesn't really go in for human rights, much less women's rights. According to Amnesty International's 2009 report on Somalia, "Aisha Ibrahim Duholow, aged 13, was publicly stoned to death on 27 October [2008] by some 50 men in Kismayo. She was convicted of ‘adultery' by a Sharia court without legal defence after she reported to local authorities that she had been raped by three men. The men were not prosecuted." Al-Shabaab justice often comes at the end of a blade. The most serious transgressors are beheaded, other miscreants have their limbs hacked off. Some are simply shot.

Going out into Mogadishu in an armoured personnel carrier with Amisom's Ugandan troops reveals the scale of the challenge they, the fledgling government and the Somali people face. With azure skies, a streaming breeze and foam-flecked seas beneath a fiery sun, Mogadishu could be a preternaturally beautiful place. Instead, the decades of fighting have reduced homes, streets and buildings to rubble. Kabul has nothing on Mogadishu in terms of being razed to ground zero. Bombed-out and shot-out shells rise from pot-holed roads and mud tracks. Cattle and goats saunter along past old men in white skullcaps and veiled women in a blaze of bright colours. There is no electricity except from generators. Government services are virtually non-existent. Squalor is the norm.

The night before the first anniversary celebration of President Sharif's administration, the ground shakes for four hours during fierce fighting between Amisom and government troops and al-Shabaab. The BBC reports at least 11 people killed. The next morning we drive across town to Villa Somalia, the presidential enclave on a modest bluff overlooking an astonishingly green city. Somali poets, singers and comedians take to the stage to entertain the president, prime minster, cabinet and assorted MPs. The joyful mood is suddenly shattered as mortars explode only metres away, killing one Ugandan and one Somali and injuring several more. An Amisom tank responds with gusto and then there are no more mortars. The show goes on. "The opposition has no programme but killing," President Sharif says later in an interview.

A couple of days later, I speak to Ismail Mahmoud, 21, a former member of al-Shabaab. He was injured in an attack against an Amisom position late last year. Two men fighting alongside him were killed. He was taken to the Amisom hospital and had his left leg amputated. There is nothing menacing about Mahmoud. He is a pitiful young man with a worn-out, hunted expression and an uncertain, unenviable future. Like so many Somalis his age, he has had no proper education. Now that his jihad is over, I ask whether he will find work and get on with his life. "When I had two legs, I was not able to find a job," he replies. "How will I be able to when I only have one?"

Although Somali society is fantastically complicated by clan histories, loyalties, divisions and strife, this latest conflict is simple at the most basic level. What it boils down to is this: al-Qaeda and its supporters are providing al-Shabaab with men and materiel. According to Major-General Nathan Mugisha, Amisom's Force Commander, they are well resourced and becoming more battle-hardened and resilient by the day. Expertise is mobile and comes from the battlefields of Afghanistan, Pakistan, Yemen and elsewhere in the Middle East. "With time, al-Shabaab is becoming a credible force," he says. "We don't need to give them this time."