More than 1,500 Syrian refugees fled to Turkey on Thursday as President Bashar al-Assad's military crackdown on protests swept up to the border, Turkish officials said on Friday.

The European Union meanwhile extended sanctions against Syrian and Iranian officials.

The local government in Turkey's Hatay province said the new wave of refugees who crossed the border on Thursday, mostly from makeshift camps just inside Syrian territory, brought the total number now registered in Turkish camps to 11,739.

Reuters reporters in Guvecci, a Turkish village at the frontier, said the camps on the other side of the border fence appeared to be completely deserted on Friday morning and they saw no more refugees crossing.

Assad's repression of the three-month old protests, in which Syrian rights groups say more than 1,300 civilians have been killed, has triggered Western condemnation and a gradual escalation of US and European Union sanctions.

On Friday the European Union announced extended sanctions on Syria, including three commanders of Iran's Revolutionary Guard accused of helping Damascus curb dissent. Syria denies Iran has played any role in tackling the unrest.

According to the EU's Official Journal, the Iranians were Major-General Qasem Soleimani and Brigadier Commander Mohammad Ali Jafari of the Revolutionary Guard, and the Guard's deputy commander for intelligence, Hossein Taeb.

Four Syrian officials were also targeted, bringing to 34 the number of individuals and entities on the list which already includes Assad and his top officials.

The United States, which has also imposed targeted sanctions on Syrian officials, said the reported Syrian army move to surround and target the town of Khirbat al-Joz just 500 metres (yards) from the Turkish border was a worrying new development.

"Unless the Syrian forces immediately end their attacks and their provocations that are not only now affecting their own citizens but (raising) the potential of border clashes, then we're going to see an escalation of conflict in the area," US Secretary of State Hillary Clinton said.

Syrian soldiers took up positions close to the border on Thursday and army armoured personnel carriers on the road crossing the hills.

Foreign Minister Ahmet Davutoglu spoke with Syrian Foreign Minister Walid al-Moualem on Thursday and Ankara summoned the Syrian ambassador, reflecting the growing disquiet in Turkey.

Turkey's 2nd Army Commander visited the Guvecci border post to take stock of the new troop deployments.

"I conveyed our concerns in a comprehensive way," Davutoglu said of his talks with Moualem as he arrived at parliament in Ankara on Friday.

At the border, only a handful of Syrian troops were visible on Friday, some occupying a prominent building at the top of the hill overlooking the border, directly across from Guvecci.

Three Syrian soldiers could also be seen at sand-bagged machine gun post established on top of a house in the Syrian border village of Khirbat al-Joz.

Mainly Sunni Turkey has become increasingly critical of Assad, who belongs to Syria's Alawite minority, an offshoot of Islam, after previously backing him in his drive to seek peace with Israel and improve relations with the US. Assad also opened the Syrian market to Turkish goods.

Clinton said she had discussed the situation with Davutoglu and that President Barack Obama had also talked to Turkish Prime Minister Tayyip Erdogan.

The US has steadily sharpened the tone of its rhetoric toward Assad, saying he is losing credibility and must either implement promised reforms or get out of the way.

Syrian authorities blame Islamist militants and armed gangs for killing more than 200 police and security personnel. It is hard to verify accounts of the violence as Syria has expelled many journalists, including Reuters correspondents.

Protests have grown in northern areas bordering Turkey following military assaults on towns and villages in the Jisr al-Shughour region of Idlib province to the west of Aleppo that had sent more than 10,000 people fleeing across Syria's 840-km border with Turkey.

Syria, a mostly Sunni country of 20 million with Kurdish, Alawite and Christian minorities is vulnerable to sectarian tensions, especially as Assad increasingly relies on loyalist Alawite troops and irregular forces known as 'shabbiha'.

Many Sunnis resent the privileges gained by Alawites who have dominated the security apparatus during the 41 years of Assad family rule. Some dislike Assad's policy of aligning Syria further with Shi'ite Iran and Lebanon's Hezbollah guerrillas.-Reuters