African Union and Somali government forces have captured the town of Afmadow, a strategic militant base in the south of the country.
Commanders say the Islamist al-Shabab group abandoned the town without a fight as their troops approached.
Afmadow is the second largest town in the south and only 115km (71 miles) from Kismayo, al-Shabab's headquarters.
Despite facing pressure on a number of military fronts, the al-Qaeda group still controls much of the country.
"Hopefully the next target will be Kismayo and then we will proceed to other towns and cities," interim Prime Minister Abdiweli Mohamed Ali told the BBC's Focus on Africa programme.
"Surely but slowly we're getting our country back from al-Shabab," he said.
'No military muscle'
Afmadow has been a key target for the Kenya troops, who make up the African Union contingent in the south of the country, since they entered Somalia last October.
Somalia analyst Mohammed Abdulahi Hassan told the BBC its importance lies in that fact that a network of roads from the town leads all over the country.
He said the militants were unlikely to have the "military muscle to retake the town from the Kenya defence forces".
A spokesman for the Kenya army, Col Cyrus Oguna, told the BBC he hoped the African Union troops would be able to take the port of Kismayo, on the main road south of Afmadow, before 20 August.
This is the date agreed by disparate Somali factions to elect a new president, ending a transitional period and the mandate of the UN-backed interim government.
Mr Hassan says if Kismayo does fall, al-Shabab will be in "a desperate position both politically and financially".
It is the second major international conference this year about how to end Somalia's two decades of anarchy.
The Horn of Africa country has had no effective central government since 1991, and has been racked by fighting ever since - a situation that has allowed piracy and lawlessness to flourish.
"The London conference focused more on unity, piracy and terrorism; Istanbul is more about development and ending the transition," Prime Minster Ali said.
Earlier this year the UN agreed to boost the AU force from 12,000 troops to nearly 18,000 to incorporate Kenyan troops which entered Somalia last October in pursuit of al-Shabab militants.
They accuse the fighters of being behind various kidnappings on Kenyan soil and of destabilising the border region.