Security has been tightened in Somalia's southwestern town of Baidoa, the seat of the transitional government, two days after an assassination attempt on President Abdullahi Yusuf Ahmed, but sources said the town was calm on Wednesday.

"It is calm now but there is an element of fear," Mukhtar Muhammad Atosh, a town resident said. "No vehicles are being allowed anywhere near the president and prime minister's residences."

There are also more security personnel on the streets. Muhammad said security forces were stopping and searching all vehicles leaving and entering the town.

Another source told IRIN that residents were worried fighting could break out between forces of the transitional government and those opposed to it, "particularly the Islamic Courts in Mogadishu".

The Union of Islamic Courts (UIC), has denied involvement in Monday's explosion in Baidoa in which 12 people died. "It is not on our agenda to kill or cause harm to Somalis," Abdirahim Ali Mudey, the UIC head of communication and information, said from the capital, Mogadishu. "We condemn such acts because they are un-Islamic."

Mudey blamed the attack on "those who want to create fear and insecurity to justify the deployment of foreign forces in our country".

Those who died in the explosion included Yusuf's brother, Jigre Yusuf Ahmed. At least 19 other people were wounded. The explosion occurred minutes after the president left a building in Baidoa housing the interim parliament.

The transitional government has appealed for help with investigations into Monday's explosion. "We have asked for help for two reasons," Abdirahman Dinari, the government spokesman, said. "First, the government does not have the expertise or the equipment to carry out such an investigation. This is the first time such a thing has happened on our soil. Second, we want to make sure that the investigation is transparent and that there will be no doubts in anyone's mind about the authenticity of the results."

Dinari said the government hoped "the international community would provide the necessary expertise to carry out a thorough investigation".

Somalia had been largely without an effective government for 16 years and the installation of the transitional government in late 2004 was supposed to end the years of chaos.

The UIC has been in control of much of southern Somalia, including the capital, since 4 June when it drove out a group of faction leaders who had controlled Mogadishu since 1991 when the administration of the late president, Muhammad Siyad Barre, was toppled.

The UIC has vowed to restore order in Somalia and has started creating Islamic courts in the areas it controls.