DAMASCUS — An airstrike hit a crowded refugee camp in Syria on Thursday close to the border with Turkey, killing at least 28 people, according to Syrian pro-opposition activists. Images posted on social media said to be of the aftermath of the strike showed at least a dozen tents burned to the ground and bloodied women and children being loaded onto a pickup truck.
The camp in Sarmada, in rebel-held territory the northwestern Idlib province, is home to between 1,500 and 2,000 internally displaced people who fled the fighting from the surrounding Aleppo and Hama provinces over the past year, according to activist Mohammad al-Shafie in the town of Atareb, about 7½ miles from the camp.
The Britain-based Syrian Observatory for Human Rights said 28 died while the Local Coordination Committees, another activist group, said more than 30 were killed. Footage on social media showed charred bodies and men pouring buckets of water on fires that erupted within the camp.
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 whether President Bashar Assad’s forces conducted the attack, but he added no US or coalition aircraft were operating in the area at the time of the strike.
Meanwhile, relative calm prevailed in the northern city of Aleppo, which has been the center of violence in recent weeks following a truce announced the day before by US officials in agreement with Russia, in an effort to extend Syria’s fragile cease-fire to the deeply contested city. The Syrian military said the truce would last only 48 hours.
Assad said in a letter to the Russian president that Aleppo will eventually be victorious, comparing the Syrian government forces’ resistance in the city to the protracted World War II battle of Stalingrad.
Syrian state media reported some violations of the Aleppo truce, saying militants fired more than 20 shells into government-held parts of the city, where 280 civilians have been killed over the past two weeks, according to the observatory group. The activist group said Thursday’s shelling killed one person.
In his letter to Vladimir Putin, which was carried on Syrian state media, Assad vowed that Aleppo and other Syrian cities and towns will defeat ‘‘the aggression’’ the way the Soviet Red Army defeated Nazi forces in Stalingrad.
‘‘Aleppo today, as well as all Syrian cities embrace the heroic Stalingrad and pledge that despite the viciousness of the aggression . . . our cities, villages, people, and army will not accept anything less than defeating the aggression,’’ Assad said.
It was unclear why Assad was making the comparison, but the rhetoric could be playing to Russian patriotic sentiment ahead of Victory Day on May 9, which marks the capitulation of Nazi Germany to the Soviet Union at the end of World War II.
Also Thursday, renowned Russian conductor Valery Gergiev led the Mariinsky orchestra from St. Petersburg in a concert at the ancient Syrian city of Palmyra, badly damaged by Islamic State extremists who held the town for 10 months.
The concert, dubbed ‘‘With a Prayer for Palmyra,’’ was to support the restoration of the UNESCO heritage site and in honor of the victims of Syria’s war. It was held in the town’s amphitheater and the audience included Russian servicemen as well as Russian sappers who have been doing demining in the town to remove bombs left by the militants.
