An air strike on a Syrian refugee camp near the Turkish border is thought to have killed at least 28 people.
Footage taken at the scene shows first responders extinguishing fires which have erupted in the impacted zone.
The strike hit a camp near Sarmada in the Idlib province of northern Syria on Thursday afternoon, according to London-based Syrian Observatory for Human Rights.
The Observatory said there were women and children among the casualites from the strike which hit the camp internally displaced people which is in rebel-held territory.
A photo posted by another opposition group, Local Coordination Committees (LCC), on their Facebook page shows at least a dozen tents burned to the ground.
The LCC put the number of people who died at more than 30.
Sarmada is home to between 1,500 and 2,000 people who have fled the fighting in the surrounding Aleppo and Hama provinces over the past year.
Foreign Secretary Philip Hammond described the attack as "appalling" and accused President Bashar al-Assad of showing contempt for the international effort to bring peace to the war-torn country.
In a statement he said: "Reports of the bombing of a refugee camp in Samarda this evening are horrifying. The Assad regime's contempt for efforts to restore the cessation of hostilities in Syria is clear for all to see.
"This attack took place against the backdrop of a concert in Palmyra, a tasteless attempt to distract attention from the continued suffering of millions of Syrians. It shows that there are no depths to which the regime will not sink. It is time for those with influence over Assad to say enough is enough."
The White House denounced the airstrike as "indefensible," with spokesman Josh Earnest saying there is "no justifiable excuse" for targeting innocent civilians who have already left their homes to flee violence.
Earnest also said it was too early to say whetherAssad's forces conducted the attack, but he added no U.S. or coalition aircraft were operating in the area at the time of the strike.
It comes as a 48-hour ceasefire in the city of Aleppo - around 27 miles from Sarmada - between the Syrian army and rebels was scheduled to begin on Thursday morning (Wednesday evening UK time).
The Syrian government's bombing campaign in the country's largest city has been described as "the worst" in the five-year conflict by the UN's political chief Jerffrey Feltman.
Aleppo has been overrun by Bashar al Assad's forces in recent weeks as they aim to gain control of the last bit of the city in rebel hands. 280 civilians have been killed so far.
But despite relative calm in Aleppo dozens more people have been killed in suicide bombs across the country, including 10 people in Homs - the country's third largest city.
Additional reporting by agencies
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