Britain has condemned an air strike on a refugee camp in north-west Syria which has reportedly left at least 28 dead.
Foreign Secretary Philip Hammond described the attack as "appalling" and accused the regime of President Bashar Assad of showing contempt for international efforts to rebuild a ceasefire.
His comments came as the White House denounced the attack on the camp in rebel-held territory near Sarmada as "indefensible".
Spokesman Josh Earnest said while it was too early to say if it was carried out by regime forces, it was thought that no aircraft from the US-led coalition fighting Islamic State (IS) had been in the area.
The British-based Syrian Observatory for Human Rights said there were women and children among the casualties.
Earlier the Mariinsky orchestra from St Petersburg staged a concert at the ancient city of Palmyra, recently liberated from IS by Syrian forces backed by air strikes from their Russian allies.
In a statement, Mr Hammond denounced the event as a "tasteless" attempt to distract attention from the country's civil war.
"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," he said.
"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."