Following reports of 10 cases from the northeast, the Syrian government has pledged to vaccinate children against polio. The government also accused rebels of attacking humanitarian aid convoys.
"We must make the vaccine available to every child in Syria, whether in a "hot" zone or a region controlled by the army," Faisal Muqdad, deputy foreign minister, told a news conference.
"We commit to this, and will grant every opportunity to humanitarian organisations to reach all Syrian children," he said.
On Tuesday the UN health agency confirmed an outbreak of polio in Syria -- which had been free of the crippling disease since 1999 -- and said it feared it would spread.
Oliver Rosenbauer, spokesman for the World Health Organisation's anti-polio division, said laboratory tests had confirmed the presence of the disease in 10 out of 22 suspected cases reported in children almost two weeks ago.
Muqdad on Monday told reporters that one reason for the outbreak was that rebels were "blocking access to basic sanitation services and even to the vaccine."
He also accused rebel groups of attacking humanitarian convoys.
"Terrorist groups have confiscated and taken aid from convoys sent to various provinces and distributed it to armed men," he said. The Syrian government refers to all rebels as "terrorists."
"We have not blocked the delivery of aid to anywhere in Syria," Muqdad said.
"But those aid groups with which we cooperate have informed us that armed men in different regions have attacked convoys heading for Aleppo," Syria's second city and former commercial hub, in the north.
The United States has accused Syrian authorities of blocking deliveries of humanitarian aid, and the opposition regularly denounces sieges of towns and villages under rebel control.
On October 25, UN aid chief Valerie Amos called on the Security Council to put "sustained pressure" on both Damascus and rebel groups to let in desperately needed aid.
She said that on top of well over 100,000 war dead, diseases, including feared new cases of polio, are spreading quickly and many people are dying "silently" from cancer and diabetes because of lack of treatment.
Malnutrition is also on the rise in Syria.
For months the opposition has denounced the siege by regime forces of areas near the capital such as Moadamiyet al-Sham, with reports of several deaths from starvation.
Hundreds of women, children and the elderly were evacuated last week from the besieged town southwest of Damascus.