The London - based Syrian Observatory for Human Rights has said a camp near Sarmada near the Turkish border was hit on Thursday afternoon and put the number of dead at 28, including women and children, and that 50 more were wounded.
The Observatory said there were women and children among the casualties from the strike which hit the camp for internally displaced people which is in rebel-held territory.
Footage taken at the scene shows first responders extinguishing fires which have erupted in the impacted zone.
A photo posted on the opposition group, Local Coordination Committees´ (LCC) Facebook page shows at least a dozen tents burned to the ground
Some reports say the attack was by Syrian or Russian warplanes but this has not been confirmed.
The strike comes a day after the extension of a truce was confirmed. The Syrian military and non-jihadist rebel forces had agreed to a temporary truce around the city of Aleppo, following pressure from the US and Russia.
A nationwide cessation of hostilities has been in place since February, but it has come under severe pressure recently, particularly around Aleppo, where some 300 people have died in clashes over the past two weeks.
The UN has warned that if the nationwide cessation fails, it will be "catastrophic" and could send 400,000 more people heading for refuge at the border with Turkey.
The Kamouna camp for the internally displaced is about 4km from Sarmada and 10km from the Turkish border.
The fighting in Aleppo early this week has been the most intense there for more than a year. The Observatory said rebels advanced into government-held western districts on Tuesday night but were pushed back by Wednesday morning.
Rebels began observing a ceasefire there on Wednesday and the Syrian military announced a 48-hour truce in the city from Thursday morning.
The nationwide partial truce agreement does not include so-called Islamic State or the al-Qaeda-affiliated Nusra Front.