"It looks apparent that, with the Ethiopian announcement that they are withdrawing from Somalia, there is nothing in the way of al-Shabab and other Islamist militias taking over the whole country."
Ethiopia had announced on Saturday that it would be pulling its forces out of the country by the end of the year.
An Ethiopian foreign ministry statement said: "This week, Ethiopian troops have begun to make preparations for their withdrawal. This has not, however, prevented continuing clashes with al-Shabab forces."
Battles have raged between Ethiopian forces and Islamist fighters for the past two years.
Fighters with al-Shabab, the armed group that has taken control of much of Somalia, told Al Jazeera that they planned to enforce Islamic law across the country.
Mohammed Adow, Al Jazeera's correspondent in Nairobi, said: "The president is echoing the frustrations of his government and the fears of millions of Somalis."
Yusuf said in an exclusive interview: "This is no peace. The al-Shabab kill anyone who speaks out. They are killers who behead innocent civilians at will. People are quiet because they fear them. They are living in terror under the Shabab.
"I don't blame Ethiopia for wanting to withdraw its troops, but if they leave, and are not quickly replaced with adequate peacekeepers; if the African Union and the United Nations do not unite to strengthen the peacekeepers in Somalia, there is no doubt al-Shabab will take over Somalia.
"And when they do, they will jeopardise the security of the whole region and beyond."
Adow reported that Yusuf's view is not supported by many Somalis, especially those living in areas under al-Shabab control - areas that used to be "where the gun was the order of the day".
"Today, they can go about their business without any fear. One such place is Kismayu, Somalia's third-largest city. Today, it is a safe place," he reported.
Relative calm has been restored to Kismayu after al-Shabab and one of its allies, the Raaskambooni Camp Mujahideen, seized control of the city from local clans three months ago.
|Al-Shabab fighters have won control of swaths of Somali territory in recent months [AFP]
Abu Ayman, the leader of the Raaskambooni Camp Mujahideen, told Al Jazeera: "We want to use Kismayu as an example and a model of our rule to the rest of Somalia.
"Our aim is to get residents in faraway towns inviting us to come and govern them according to the way of Allah. The calm in Kismayu has benefited its down-trodden most."
Most of Kismayu's residents agree with Abu Ayman, saying they are now able to go about normal life without fear of attacks by marauding gangs of armed men who had terrorised them periodically for nearly 18 years.
"I remember times when young boys with knives used to rob us of our daily earnings. Now we can carry lots of money without any fear of being robbed," Mohammed Fundi, a porter and Kismayu resident, said.
Seyyid Ali, also a porter in the city, said: "We used to be sort of enslaved. When we load six lorries, we used to be paid for just one or two. Today we get wages equal to our output. We have justice here."
Peace, at a price
But our correspondent said the apparent peace had come at a price.
"International aid agencies, the lifeline of Somalia's poor, fled the town because of the fighting.
"They have still not returned as the Islamists have little tolerance for anything - or anyone - foreign," he said.
"The suffering is huge as the poor are largely left to fend for themselves."
Kismayu has been left with one hospital to serve the needs of nearly one million people from the city and surrounding areas.
The hospital used to be run by Medecins Sans Frontieres, which was forced to abandon the centre eight months ago after members of staff were killed by fighters.
Now, it is common for only one doctor to be on duty at a time, and medical supplies are dwindling.
Adow described the people of Kismayu as "numb to the myriad problems surrounding them".
"We used to be sort of enslaved... today we get wages equal to our output. We have justice here"
Seyyid Ali, porter and resident of Kismayu
"They [residents] have survived the vagaries of war. They have weathered the almost 20 changes in Kismayu’s administrations over the past 18 years and its people have learned to live with and obey any group that has the upper hand," he said.
Somalia has had no effective government since a coup removed Siad Barre from power in 1991, leading to an almost total breakdown in law and order across most of the country.
The only relative stability experienced by some parts of the country came during the brief six-month rule of the Islamic Courts Union in 2006.
However, they were driven out of the capital, Mogadishu, and other areas, by Ethiopian and government troops – sparking an upsurge in fighting.
Ethiopia is due to remove its troops from war-torn Somalia by the end of the year.