Britain formally recognised a newly-formed opposition bloc as the sole representative of the Syrian people, as UN head Ban Ki-moon said he feared Syria could become a "regional battleground."
Britain's recognition of the opposition National Coalition came as fighting raged across Syrian flashpoints, including in the northern town of Ras al-Ain where a watchdog said dozens died in clashes between rebels and a Kurdish militia.
Turkish Foreign Minister Ahmet Davutoglu said meanwhile that NATO member Ankara, a sharp critic of President Bashar al-Assad's regime, would formally ask the alliance for Patriot missiles to protect its border with Syria.
In announcing Britain's recognition of the National Coalition formed in Doha on November 11, Foreign Secretary William Hague told parliament he took the decision after leaders of the bloc he met in London assured him that they have backing inside Syria and would respect human rights.
Hague said he has asked the group to appoint a political representative to Britain and he announced an increase in aid and support for the coalition as it battles Assad's regime.
Last week, France became the first Western country to recognise the coalition and on Monday the European Union said it "considers them legitimate representatives of the aspirations of the Syrian people."
UN Secretary General Ban, on a visit to Cairo, cautioned Tuesday that on the ground there was potential for the conflict to spin out of control.
"We are deeply concerned about the continued militarisation of the conflict, horrendous violations of human rights and the risk of Syria turning into a regional battleground as the violence intensifies," he told reporters.
Ban also urged donor countries "to generously contribute" to humanitarian programmes inside Syria and help Syrian neighbours which have taken in tens of thousands of refugees.
And Turkey, which is hosting more than 120,000 Syrian refugees, said it would formally ask its NATO partners for Patriot anti-missile systems to protect its border.
"(Patriots) are a precautionary measure, for defence in particular," Davutoglu told reporters. "We will submit the formal request as soon as possible."
Over the past several months, Turkey has steadily reinforced its border defences, notably after five of its nationals were killed by artillery fire from Syria in October.
-- Rebel intelligence service -- --------------------------------
Signup to our newsletter and follow us on Facebook and Twitter!
Rebels, meanwhile, announced Tuesday the creation of a security service to "defend the Syrian revolution" in a country that has been awash with feared intelligence agencies for the past five decades.
Its objective is "to be a powerful security shield to protect the sons of the revolution from attacks, arrests and killings," and to hunt down members of the opposition who have committed abuses, they said in a video statement.
On the ground Syrian troops besieged the town of Daraya near Damascus and pounded it with shells, killing a woman and a child, in a fresh attempt to storm it, activists and a watchdog said.
"We have been under constant rocket and artillery fire," Abu Kinan, an activist from Daraya, told AFP via Skype, adding that troops had ringed the area with checkpoints and arrested scores of people.
Initially considered a heartland of non-violent activism, Daraya was the site of the worst massacre in Syria's 20-month conflict, with more than 500 people killed there in late August, according to monitors.
The Syrian Observatory for Human Rights also reported that 29 people had died over the past 24 hours in clashes between Kurdish militiamen and rebels in the northern Syria town of Ras al-Ain, near the Turkey border.
The casualties over the past day included four Kurdish fighters, a local Kurdish official, and 24 members of the Islamist Al-Nusra Front and Gharba al-Sham rebel battalions, Observatory director Rami Abdel Rahman told AFP.
Rebel fighters also attacked the Sheikh Suleiman air defence battalion west of Aleppo city, the Britain-based Observatory said, and a rebel source reported fierce clashes around the base.
The clashes came less than two days after a military source said the insurgents took control of the sprawling Base 46 in the same province.
The Observatory puts the death toll in more than 20 months of conflict at more than 39,000. On Tuesday, at least 61 people were killed across Syria, it said.
The Friends of Syria group which supports the opposition is to meet in the southern Moroccan city of Marrakesh on December 12.
Diplomatic sources in Rabat said US Secretary of State Hillary Clinton would be among those attending.
The meeting, which had been due to take place in October, follows previous meetings of the group in Tunis, Istanbul and Paris, bringing together senior officials from countries supporting the opposition to Assad.