Story highlights Clashes are a sign of weakened regime in the capital says expert

Regime had a tight grip there but new jihadist group is asserting its strength

(CNN) Rebel groups who launched a surprise attack in northeastern Damascus were taking advantage of Syrian regime forces being overstretched by fighting elsewhere in the country, an expert on the region said.

The clashes -- which broke out Sunday in the Syrian capital -- were reported by opposition groups, the Syrian Observatory for Human Rights and Syrian state media.

Damascus has not seen such attacks in months if not years, said SOHR Director Rami Abdel Rahman.

Since the start of the conflict, the Syrian regime and allied militias have held a tight grip on the capital. The opposition has only a few pockets of control around Damascus, including a part of the district of Jobar. The rebel fighters began the attack from that area of the city.

The assault was led by Islamist groups including Ahrar al-Sham and the recently formed umbrella jihadist group Hayat Tahrir al-Sham. That group includes another -- Jabhat Fatah al-Sham.

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