The main road from Somalia's capital, Mogadishu, to the strategic south-western city of Baidoa has been totally recaptured from Islamist militants, African Union (AU) troops have said.
It is the first time the cities have been linked in more than two years.
The AU is helping a new UN-backed government regain territory from al-Qaeda-aligned insurgents.
The al-Shabab group has been forced out of main towns but still controls most villages and rural areas.
The last section of the 241km- (149 mile-) road from Mogadishu to Baidoa was successfully secured on Monday, said the African Union mission in Somalia, which has 18,000 troops in the country.
"This significant move not only allows for free movement of the population, but also opens up this key supply route and allows for the provision of humanitarian aid," it said in a statement.
Meanwhile, there has been an explosion in Mogadishu at the main office of Dahabshiil, one of the largest money transfer companies in Africa.
The BBC's Mohamed Mwalimu in the city says the doors were ripped off at the office in Bakara market, and at least one person was injured.
It was not clear who was behind the explosion but the firm had threatened to close down its branches in areas held by al-Shabab, he says.
Security has improved in Mogadishu since al-Shabab withdrew from the city in August 2011, but its fighters still launch attacks.
For more than 20 years Somalia has seen clan-based warlords, rival politicians and Islamist militants battling for control of the country.