The Union of Islamic Courts (UIC) has denied reports that it has captured a port on Somalia's central coastline.
The Islamist militia are making gains across Somalia
Eyewitnesses in Hobyo town said earlier that heavily armed UIC militiamen moved in at dawn without any fighting.
But Islamist leader Sheikh Hassan Dahir Aweys told the BBC that neither he nor his fighters had entered the town.
The Islamists have taken control of most of central and southern Somalia since seizing the capital in June after defeating an alliance of warlords.
Attempts to get the transitional government and Islamic courts to go to Sudan for peace talks have so far failed.
The town of Hobyo is close to the autonomous Puntland region, whose administration is hostile to the Islamic courts.
It has warned its population against supporting the Islamist advance.
The BBC's Somalia service editor, Yusuf Garaad Omar, says the town does not have an existing Islamic court, but it is likely that the UIC has supporters in the town.
According to reports on the Somali Shabeelle website, the Islamist militia travelled on armed pick-ups into Hobyo at dawn.
"We did not capture it but we reached the people of Hobyo to bring them our message of peace," an Islamic officer who wanted to remain anonymous told AFP news agency.
"First, the Islamist army technicals surrounded the town, then they sent an envoy to negotiate, before their entry was accepted," local leader Hussein Jimale told Reuters news agency.
But these reports were denied by Mr Aweys on the phone to the BBC Somali service.
At the weekend the UIC took control of Harardhere and Eldher ports - both of which have been used as a base for piracy.
Ghedi is now wanting to talk to the Islamic courts
The internationally recognised interim government controls only the central town of Baidoa, but is supported by Ethiopia, which says it will intervene if Baidoa is attacked.
The Islamists also claimed some 100 government fighters defected on Wednesday to Burhakba from Baidoa with seven armed pick-up trucks.
Interim President Abdullahi Yusuf is from Puntland and is a long-time ally of Ethiopia.
His prime minister, Ali Mohammed Ghedi, has said the government will now participate in peace talks, after earlier being reluctant to enter dialogue with the UIC, a stance that led to mass resignations from his government.
But the UIC refuse to go to the Sudanese capital, Khartoum, for talks unless all Ethiopian troops leave Somali soil - though Ethiopia denies any of its troops are in Somalia.
A visiting Kenyan delegation recently urged the UIC to avoid any escalation of hostilities in Somalia and take part in talks.
Somalia has had no effective central government since the ousting of dictator Siad Barre in 1991.
Meanwhile, a United Nations agency has warned that a severe humanitarian crisis could erupt this year in Somalia, where insecurity could compound crop failures and livestock deaths during drought - with the central and southern areas worst hit.
The UN's Food Security Analysis Unit (FSAU) said some 1.8m Somalis remain dependent on assistance but warned that the number could double if fears of widespread conflict are realised.
It said supplies of aid and imported food stuffs were compromised by violence and could be reduced to a trickle by large-scale fighting.