Official: Suicide bombing in Syrian town kills 6

Iran is one of Syrian President Bashar Assad's main allies. Tehran has provided his government with military and political backing for years and has kept up its support since the uprising there began in March 2011.

Meanwhile, Syria said that it will work with international organizations to ensure that all children in the country, even those in rebel-held areas, will be vaccinated against polio following an outbreak of the crippling and highly communicable disease.    

The World Health Organization last week confirmed 10 cases of polio among babies and toddlers in northeastern Syria. The UN health agency warned that the outbreak the first in 14 years in the country  risks spreading among an estimated half-million Syrian children who haven't been immunized because of the civil war.    

"We intend to vaccinate each Syrian child regardless of the area they are present in, whether it is a hotspot or a place where the Syrian Arab Army is present," deputy foreign minister Faisal Mekdad said. "We promise that we will give opportunity to humanitarian organizations to reach every Syrian child."      

Mekdad did not specify when the immunization campaign would begin, or how those administering the vaccinations would reach rebel-held areas.      

Syria announced last month that it had launched a vaccination campaign, while UNICEF Executive Director Anthony Lake said his organization and the WHO planned to immunize 2.4 million children throughout Syria. Access to all areas of the country, however, remains a problem.             

Aid groups have called for cease-fires to allow immunization campaigns to reach zones affected by fighting. There is some precedent: Syria's warring parties have struck temporary truces before to allow civilians to flee and aid to enter some areas. International chemical weapons inspectors also have managed to cross front lines.

The need to address the polio threat is urgent, health officials say. The virus usually infects children in unsanitary conditions through consuming food or drink contaminated with feces. It attacks the nerves and can kill or paralyze, spreading widely and unnoticed before it starts crippling children.

With huge numbers of Syrians still fleeing the violence to seek safety abroad, the risk of an outbreak in countries that have absorbed the bulk of refugees Lebanon, Jordan and Turkey is high.