Rebels fighting President Bashar al-Assad's regime have seized a 25-kilometre (15-mile) strip of land stretching from the Jordan border to the Israeli-occupied Golan Heights, a watchdog said on Sunday.
In the northern province of Aleppo, at least 10 civilians were killed in an air strike, while mortar rounds crashed int the building housing state television and radio offices in Damascus, said the Syrian Observatory for Human Rights.
"Fighters loyal to Al-Nusra Front, Al-Yarmuk Brigade, Al-Mutaz Billah Brigade and others took control of Al-Rai military checkpoint," east of Sahem al-Golan town in the southern province of Daraa, the Observatory also reported.
"The fighters seized the site after regime forces retreated. The 25-kilometre area located between the towns of Muzrib (near the Jordanian border) and Abdin (in the Golan) is now out of regime control."
The Britain-based Observatory said the rebels had on Saturday seized a key air base in Daraa after two weeks of fierce battles with loyalist troops.
The reports came as Israel's new Defence Minister Moshe Yaalon vowed an "immediate" answer to all Syrian gunfire onto the Golan Heights.
Yaalon issued the warning shortly after Israeli troops on the strategic plateau shot at an Syrian army post after coming under fire for the second time in 12 hours, according to the Israeli army.
"We see the Syrian regime as responsible for every breach of sovereignty. We shall not allow the Syrian army or any other body to violate Israeli sovereignty firing into our territory," Yaalon said in a statement.
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It was not immediately clear whether the shooting was from the Syrian army or rebel forces in the area.
The rebel advances came days after insurgents seized a border crossing on the frontier with Jordan, said the Observatory.
Also on Sunday, at least 10 civilians, among them four children aged under 16 and a woman, were killed in an air strike on the village of Akhtarin, said the Observatory.
Amateur video filmed by activists and distributed by the Observatory showed a crowd of people running towards the site of the air strike, as a tower of smoke rose up into the sky.
"Guys, help us, we need to get them out of there," said one resident in the footage.
In the heart of Damascus, "several mortars hit the building housing the General Television and Radio Authority, behind the ministry of education," said the Observatory.
State news agency SANA blamed "terrorists", the regime's term for rebels, for the mortar attack, reporting that 10 civilians were wounded in the "new attack on Syrian media."
The United Nations estimates that violence across Syria has killed at least 70,000 people since the conflict erupted in March 2011. The Observatory said at least 104 people were killed on Sunday alone, among them 61 civilians.