Human Rights Watch's statement came Tuesday as the Security Council is expected to meet later in the day for a fifth round of reporting on the resolution.
February's resolution demanded a halt to all attacks against civilians and indiscriminate shelling and aerial bombardment, including the use of barrel bombs, in populated areas.
HRW says it has documented over 650 strikes on rebel-held neighborhoods in the northern Aleppo since the resolution's adoption.
It noted that opposition fighters also participate in indiscriminate attacks, including mortar strikes and car bombings.
Activists say barrels bombs on Aleppo have killed more than 2,000 people this year. AP