The World Health Organization (WHO) says that since the re-emergence of the disease in July last year, 200 children in Somalia have been paralyzed with polio.
Polio is caused by a viral infection involving the brain and spinal cord, and can paralyze a child for life within hours.
In only 10 percent of cases is a full recovery seen.
The WHO says two new cases of poliomyelitis have been reported from two new regions: Lower Juba, southern Somalia and Mudug region, northeastern Somalia.
These regions, with security-related restrictions, present a risk to neighbouring countries.
The cases also threaten the progress made in Mogadishu, formerly the epicentre of the outbreak which has affected a total of 199 children to date, but which appears to be on the decline in the city.
The United Nations agency says a nationwide vaccination campaign is being launched on Sunday 26th March to try to reach 1.4 million Somali children under age five, in an effort to halt the further spread of the virus and protect the gains made in Mogadishu.
Four in five of the cases since July were recorded in the capital Mogadishu, where the virus now seems to be on the decline after immunization campaigns.
In total the virus has now been reported in eight of Somalia's 19 regions, says WHO spokesman Oliver Rosenbauer, and it is considered to be a large outbreak.
Somalia is the 19th country to be re-infected with polio in the last two years triggered by Nigeria's northern state of Kano suspending immunizations in 2003, which allowed the virus to spread to neighboring countries.
Vaccinations in Nigeria were resumed after a 10-month ban imposed due to religious leaders accusing them of causing sterility, was lifted.
A worldwide campaign launched in 1988 by the WHO to eradicate polio, failed to reach its target of halting transmission worldwide by the end of 2005.