At least six people have been killed in fighting in Baidoa, where Somalia's transitional government is based.
Government forces have now taken control of the city airport from militia who had been controlling it, the BBC's Mohammed Olad Hassan reports.
The clan-based militia had previously demanded taxes from airport users.
The clash erupted after a group of police officers tried to leave the airport for training in Kenya, and the militia demanded they pay taxes.
The police commander sent his forces to the airport early on Monday morning to expel the clan-based militia, who had been demanding $20 from each passenger and $100 for each plane using the airport.
Our correspondent says at least seven people have been wounded in the fighting, in addition to those killed.
The transitional government controls only a small area around Baidoa.
A long-delayed second round of peace talks began in Khartoum at the weekend between the government and the powerful Union of Islamic Courts, which controls a large part of southern Somalia including the capital, Mogadishu.