UN Secretary-General Ban Ki-moon has said he fears the 20-month-old conflict in Syria could turn the country into a regional combat zone.
Ban spoke in Cairo after talks with Arab League Secretary-General Nabil Elaraby.
"We are gravely concerned about the continued militarization of the conflict, horrendous violations of human rights, and the risk of Syria turning into a regional battleground as the violence intensifies," Ban said.
He also highlighted the plight of Syrian refugees.
"The humanitarian situation in Syria continues to deteriorate. More civilians are being displaced within Syria, and an increasing number of Syrian refugees are seeking safety in neighboring countries," he said. "I remain grateful to Syria's neighbors for the effort to accommodate and care for them."
The UN secretary-general also called for more international humanitarian aid for Syria.
There are more than 400,000 registered Syrian refugees in neighboring countries, mostly in Turkey, Jordan, and Lebanon.
Meanwhile, Britain has become the latest Western country, joining France and Italy, to officially recognize the newly formed Syrian National Coalition opposition group.
Foreign Secretary William Hague made the announcement to parliament in London.
"On the basis of the assurances I received in my consultations with the European partners yesterday, her majesty's government has decided to recognize the National Coalition of Syrian Revolution and Opposition Forces as the sole legitimate representative of the Syrian people," Hague said.
In Ankara, Foreign Minister Ahmet Davutoglu said that Turkey is prepared to officially ask NATO to supply it with Patriot surface-to-air missiles to counter a potential threat from Syria.
"Intensive work is under way on the Patriot [surface-to-air] missile [discussions] and the talks have reached the final stage, considering all possibilities and risks," Davutoglu said. "A formal request [to NATO] will be submitted as soon as possible and this process will be officially completed."
NATO Secretary-General Anders Fogh Rasmussen said on November 19 that NATO would consider Turkey's request as a matter of urgency.
In Damascus, mortars hit Syria's Information Ministry building on November 20, causing some damage but no casualties.
With reporting by Reuters, AP, and dpa