Syrian government forces made advances on Sunday in the town of al-Nabk, one of the last rebel-held areas in Qalamoun region bordering Lebanon, a watchdog said Al Arabiya reported
"There is fierce fighting in al-Nabk between government forces, backed by Lebanese Hezbollah fighters, and al-Nusra Front and the Islamic State of Iraq and the Levant," the Syrian Observatory for Human Rights said, according to Agence France-Presse.
President Bashar al-Assad's troops have taken "new sectors of the town," said the monitor, which sources its information from field-based activists and medics.
Assad's forces have encircled and bombarded the town, which lies northeast of the capital Damascus, for the past two weeks.
"The Syrian army is continuing to rake orchards in al-Nabk, and has discovered a terrorist [a reference to rebel groups] lair containing medical equipment and drugs," state television said, as quoted by AFP.
On Saturday, at least 40 bodies of men, women and children were discovered in the town after heavy shelling by the regime's army, the Syrian National Council, an opposition group, reported.
Taking the al-Nabk area would solidify the Syrian regime's control, linking Damascus province with Syria's central Homs province.
Meanwhile, regime air raids on the jihadist-held town of Raqqa in north of Syria have killed 18, the monitor said, updating its earlier figure of 14.
Among the dead were five women and six people under the age of 18, the group said.
Raqqa, which is the capital of the province of the same name, is the only major urban center to fall entirely under opposition control since the Syrian conflict began in 2011.
Also on Sunday, Lebanon's state-run news agency said troops captured three Syrian gunmen in Lebanon as they attempted to cross the border toward a contested region in Syria, according to the Associated Press.
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