He returned alone to their flat on the 14th floor, where he was trapped for two hours.
Omar, 25, made it out and is being treated for smoke inhalation in hospital, according to friends and family.
Tributes have been paid to a "kind and charitable" refugee who was named as one of the first victims of the devastating Grenfell Tower blaze.
He said: "Mohammed undertook a risky journey to flee war and death in Syria, only to meet it here in the United Kingdom, in his own home".
Mohammed al-Haj Ali fled from Syria and settled in the United Kingdom in 2014.
After being overwhelmed by smoke, Mohammad was forced to return to the apartment, where he called family and friends to say goodbye, Hourani said.
The charity called for a "thorough investigation" into building regulations, adding: "Mohammed came to this country for safety and the United Kingdom failed to protect him".
"Our thoughts and deepest sympathies are with his family and friends".
The 23-year-old came to Britain from his war-torn home in Daraa, Syria, three years ago.
Investigators said on Wednesday they do not want to speculate into the cause of the fire.
Mr Alhajali's brother Omar Alhajali was also caught up in the blaze, but managed to escape.
"It's just really sad, he left Syria running away from death and looking for a better life", said Hourani.
The University of West London addressed the death in a statement, saying they were "shocked and saddened" by the tragic incident, HuffPost UK reported. Commander Stuart Cundy said 17 people are now in critical condition and police are seeking to identify and locate the people who continue to be missing.