"The Committees for the Protection of the Kurds (YPG) have taken over the Manajeer area, scene of battles with the Islamic State of Iraq and the Levant (ISIL), Al-Nusra Front and other rebel groups," the London-based Syrian Observatory for Human Rights said on Tuesday.
The capture of Manajeer left the whole of the area around the strategic border town of Ras al-Ain in Kurdish control, the group said.
The advance came a day after reports that Kurdish fighters had driven terrorist groups out of 19 towns and villages across northeastern Syria, and a week after they captured the key Iraqi border crossing at Yaarubiyeh.
The al-Qaeda-linked militants "have now lost their last remaining positions in the countryside of Ras al-Ain," the Observatory said.
The Al-Qaeda loyalists withdrew to the city of Raqa in the Euphrates valley to the southwest, the only provincial capital outside government control, and now dominated by ISIL.
Near the capital, the army pressed its offensive against rebel enclaves, hitting the town of Mleiha east of Damascus with a ground-to-ground missile, the observatory said.
Amateur video posted online by activists showed a huge cloud of grey smoke rising above the town.
Southeast of Damascus, the militants shelled the majority Christian-Druze suburb of Jaramana, a government-held area that has come under repeated rebel attack, the group said.
In the central province of Hama, ISIL militants captured a rebel commander and more than 20 fighters in the latest infighting between the insurgents and mainstream rebels, the group added.