* Syrian activists say 12 killed
* Turkey scrambles jets
* Ankara has asked for NATO missiles (Adds death toll, details)
DIYARBAKIR, Turkey, Dec 3 (Reuters) - Syrian government forces bombed rebel positions in the frontier town of Ras al-Ain on Monday, killing at least 12 people according to opposition activists, and prompting Turkey to scramble fighter jets along the border.
The Syrian Observatory for Human Rights said six of those killed by the air raids on the town's Mahatta neighbourhood were rebel fighters and that 30 people were wounded.
Heavy bursts of anti-aircraft fire shook the Turkish town of Ceylanpinar, which abuts Ras al-Ain, sending residents fleeing for cover. Columns of smoke rose up from the Syrian side and ambulances rushed the wounded to hospital.
Security sources said Turkish F-16 jets were scrambled from their base in the southeastern city of Diyarbakir after the air raids on the rebel Free Syrian Army's headquarters in Ras al-Ain, in a warning to Damascus not to breach Turkish territory.
Rebels overran the town almost a month ago in fighting which has triggered some of the biggest refugee movements of Syria's 20-month-old civil war, and has tested Turkey's resolve to defend itself against any spillover of violence.
Shells landed in Ceylanpinar during Monday's fighting, the security sources said, although it was not immediately clear whether they were fired by forces loyal to President Bashar al-Assad or by the rebels.
Turkey, a main backer of Syria's opposition, has asked NATO for Patriot surface-to-air missiles to be positioned near its 900-km (560-mile) border with Syria as a defensive measure.
It has repeatedly fired back over the border in response to stray shells and gunfire flying into its territory.
Ankara is concerned about its neighbour's chemical weapons, the growing refugee crisis on its border, and what it says is Syrian support for Kurdish militants on its soil.
(Reporting by Seyhmus Cakan in Diyarbakir and Erika Solomon in Beirut; Writing by Nick Tattersall; Editing by Angus MacSwan)