Thirteen people were killed in Syria's Hama province on Wednesday when troops fired on a car and provoked a reprisal ambush, activists said, the latest bloodshed in a nine-month-old uprising against President Bashar al-Assad.
The British-based Syrian Organisation for Human Rights said army deserters ambushed a convoy of four military jeeps, killing eight soldiers, in response to the army attack on a car which killed five people.
The United Nations says more than 5,000 people have died in Assad's crackdown on protests that erupted in the southern city of Deraa in March, inspired by Arab uprisings elsewhere.
Assad, 46, whose minority Alawite family has held power in majority Sunni Muslim Syria for four decades, faces the most serious challenge to his rule from the turmoil.
The demonstrations started with peaceful calls for reform but burgeoned into demands for Assad's overthrow. A growing armed insurgency has since fuelled fears of civil war.
The Syrian government says more than 1,100 members of the army, police and security services have been killed. State media give daily reports of military funerals as well as frequent clashes with armed groups and discoveries of explosives.
The United States and France, which blame Assad's forces for the violence, have urged the United Nations Security Council to respond to the mounting death toll.
But Syria still has international allies. Russia and China have blocked Western efforts to secure Security Council condemnation of Damascus and on Wednesday its closest regional ally Iran sent signals of support this week.
State news agency SANA reported the visiting Iranian minister for urban development and roads, Ali Nikzad, as saying his country would stand by Syria and support its economy and its stances facing the great conspiracy targeting it.
SANA said Nikzad's visit to Damascus followed the endorsement by Iran's parliament on Tuesday of a free trade agreement between the two countries.
IRAN SUPPORT CRUCIAL
Iranian economic support could be crucial for Syria, facing sanctions from the United States, European Union, neighbouring Turkey and the Arab League. Syria's economy has already been hit by a collapse in tourism and oil revenues, falling trade, a weakening currency and a halt in foreign investments.
Despite the worsening economic crisis and a growing number of army defections, mainly among Sunni conscripts, Assad still has the loyalty of most of the army. Unlike in Libya, the rebels have secured neither high-level defections from the military or government, nor do they fully control any territory.
The city of Homs, about 150 km (95 miles) north of Damascus, is the main centre of opposition to Assad. United Nations human rights chief Navi Pillay said on Monday there were extremely alarming reports of a troop buildup around Homs which might signal an imminent assault on the city.
Briefing the U.N. Security Council, she said the 5,000 people killed in Syria include civilians, army defectors and those executed for refusing to shoot civilians, but not soldiers or security personnel killed by opposition forces.
In Washington, State Department spokeswoman Victoria Nuland said on Tuesday: We think it's high time for the U.N. to act. We thought it was when (Russia) vetoed, and we think it is all the more necessary now.
The violence spilled over into Lebanon on Wednesday when residents said Syrian soldiers crossed the frontier into the Bekaa Valley and fired at local shepherds, wounding two of them.
A media rights group said on Tuesday Syrian authorities had charged U.S.-born Syrian blogger Razan Ghazzawi, who was arrested as she tried to leave for Jordan last week, with seeking to incite sectarian strife.
(Additional reporting by Erika Solomon; Editing by Alistair Lyon)