Ali Daqneesh, the 10-year-old brother of Omran Daqneesh
, died Saturday, according to Yousef Saddiq, the director of the Aleppo Media Center.
Ali succumbed in an Aleppo field hospital from injuries sustained in the Wednesday airstrike, Saddiq said.
"He was in critical condition for the past three days and passed away this morning," Saddiq said. "His mother is still receiving medical care because she is also in critical condition."
The family remains in Aleppo, he said.
The photos and video of Omran sitting silently in an ambulance awaiting help are grim reflections of the grinding Syrian civil war.
The image spread across social media and sparked interest in the situation in Aleppo, much like the picture of a child's body on a Turkish beach
raised sympathy for refugees who fled Syria.
"Omran ... is still alive, and God willing will continue his life in better conditions than the ones he is living in now," said a doctor who identified himself as Dr Abu Rasoul, who treated the deceased.
"His brother, whose photo was not taken, no one mentioned him, he died and he is by God's side now."
The doctor said Ali suffered a lot of trauma.
"Omran was pulled out of the rubble quickly to come back to life, Ali stayed under the rubble for a while," he said.
Death toll climbs in Aleppo
Aleppo, in northern Syria, has been besieged for years during that country's civil war. Fighting has intensified in recent weeks and the death toll is climbing.
Ali's death raised to 448 the number of people killed
by fighting in and around Aleppo this month alone, reported the London-based Syrian Observatory for Human Rights. That number includes 100 children.
More than 12,500 people, including more than 4,500 children, were killed over a 22-month period by Syrian and Russian air bombardment, the SOHR reported.
Bombing and years of warfare have reduced large sections of Aleppo to rubble. The International Red Cross said the city is on the brink of a humanitarian crisis.
Aleppo has strategic importance
as the country's largest city and a vital economic hub. When rebels first launched their attack on the city in July 2012, it sent shock waves through government-held parts of Aleppo. Regime strongholds were no longer seen as impenetrable. Now the Syrian military, aided by Russia, is bombing the city in an attempt to win it back.
Former ambassador criticizes Russia
Activists blame the Syrian regime and Russia for the bombings in Aleppo.
Russia, however, has consistently denied it is bombing civilians
in Syria, saying it only targets militants.
For instance, 50 people were killed in April when a hospital near Aleppo was bombed
. Despite accusations, Russia and Syria said they didn't drop those bombs.
Reports that ties between the United States and Russia are growing stronger and could extend to collaboration on airstrikes against targets inside Syria has drawn criticism from former US Ambassador for War Crime Issues Stephen Rapp.
In an interview with CNN's Hala Gorani on Thursday, Rapp complained of "massive violations of humanitarian law and war crimes."
"(If) we get involved in joint operations with people that are committing war crimes," he said, "I don't think it's a smart bargain. It puts us on the wrong side. We need to continue to press for accountability and to work with people that don't have blood on their hands."
He referred to the boy in the picture, saying: "People say we have to unite against Deash (another term for ISIS), but how can someone who did what they did to Omran be a useful individual?"