At least 15 people died in violence across Syria on Sunday, activists and state media said, as the visiting Red Cross chief sought access to those detained in five months of anti-regime protests.
Six soldiers and three civilians were killed when an "armed group" opened fire on a bus in Maharda, central Syria, state news agency SANA reported.
"Nine people, among them an officer, were killed and 17 others wounded this morning in Maharda in an ambush by an armed group who opened fire on a bus carrying soldiers and labourers going to work," it said.
SANA said a security patrol killed three of the assailants and seriously wounded a fourth.
The Local Coordination Committees (LCC), which groups anti-regime activists on the ground, said security forces shot dead three people in the Khan Sheikhwan area of Idlib province in northwest Syria.
Security forces encircled hospitals "to prevent the wounded from being brought in for treatment," it charged.
On Friday, SANA said gunmen in Khan Sheikhwan had kidnapped a corporal with Syria's internal security services, Wael Ali.
International Committee of the Red Cross (ICRC) chief Jakob Kellenberger flew into Damascus on Saturday for talks with President Bashar al-Assad over access to prisoners and areas of unrest.
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According to activists, 27 people were killed in operations by the army and security services across Syria on Friday and Saturday.
The latest bloodshed came as European ministers warned of more sanctions in addition to an oil embargo over Syria's defiance of mounting international calls to halt a deadly crackdown on anti-Assad protests.
More than 2,200 people have been killed in Syria since almost daily protests began on March 15, according to the United Nations, while human rights groups say more than 10,000 people are behind bars.
Apart from the oil embargo which went into effect on Saturday, the EU expanded a list of around 50 people, including Assad, targeted by an assets freeze and travel ban.
The embargo is aimed at depriving Assad's regime of a vital source of cash as the EU buys 95 percent of Syria's crude exports.
EU foreign policy chief Catherine Ashton warned on Saturday that the European Union would "continue to put the pressure on and to look for ways of doing so."
The ICRC delegation chief in Damascus said Kellenberger would stay in Syria until Monday afternoon and meet with Assad, Prime Minister Adel Safar and Foreign Minister Walid Muallem.
His office said that during a previous visit in June "an understanding was reached" for "enhanced access to areas of unrest, and negotiations would take place concerning ICRC visits to detainees."
Asked about the possibility of visiting detainees, the ICRC delegation chief in Damascus, Marianne Gasser, said: "We are confident that we will be able to start visiting people detained by the interior ministry."