Egypt's government has said that it was an explosives-laden car belonging to a violent breakaway faction of the Muslim Brotherhood that blew up outside a cancer hospital in central Cairo, killing 20 people and injuring 47 in one of the deadliest terror incidents in years in the Egyptian capital.
Authorities said the blast and subsequent fire took place shortly before midnight on Sunday when the car veered into a one-way street and collided with oncoming traffic.
The impact set off the explosives, igniting a large fire and causing significant damage to the hospital and nearby buildings.
The victims are believed to include motorists, passengers and pedestrians.
On Monday, Egypt's Interior Ministry said that the car's cargo of explosives was destined for use in a terrorist attack elsewhere.
It did not give a reason for the driver's decision to drive against traffic on a one-way street.
The UAE condemned the attack and reiterated its opposition to any form of terrorism.
"This heinous act of terrorism is completely against all religious and humanitarian values and principles," the UAE Ministry of Foreign Affairs and International Co-operation said on Monday.
Video posted by Egyptian authorities showed a grey sedan moving against traffic, with other cars swerving to avoid it. The clip ends with the blast and a large orange ball of fire.
The Interior Ministry said the explosives-laden car was reported stolen from the Nile Delta province of Menoufiya months ago.
"Preliminary findings showed that the 'Hasm' movement that belongs to the terrorist Muslim Brotherhood is behind the rigging of the vehicle as a prelude to carrying out a terrorist attack by one of its members," the ministry said.
Egyptian President Abdel Fattah El Sisi on Facebook offered his condolences to families of the victims of the "terrorist and cowardly" attack.
Mr El Sisi also wished the injured a speedy recovery and repeated his government's resolve to "uproot" terrorism.
As a general, he led the military overthrow in 2013 of Mohammed Morsi, a president from the Muslim Brotherhood, whose one year in office proved divisive.
Mr Morsi's removal took place amid mass protests against his rule.
Mr El Sisi was elected president a year later and has since overseen a crackdown to dismantle the Brotherhood.
Hasm took up arms against the government shortly after Mr Morsi's removal and is blamed by authorities for a string of terrorist attacks.
The cancer hospital said two of its security guards were among those killed in the Cairo blast, but that no member of its staff or patients were among the victims.
The National Cancer Institute has three buildings overlooking a narrow stretch of the Nile that runs by the eastern shore of the river island Manial Al Rhoda.
The main building, a seven-storey structure that houses patients and operating theatres, was violently shaken by the explosion.
The blast shattered windows, knocked out lifts and damaged equipment and furniture. The facade of the building was considerably damaged.
Images posted online showed bodies lying motionless on the ground, cars ablaze and people screaming in horror.
Witnesses spoke of bodies caught in flames, flying glass and passers-by taking the injured to ambulances.
"I was sleeping at home when the blast shook my building and glass flew everywhere," said one witness who lives about 200 metres away from the site.
The explosion was clearly heard throughout the entire neighborhood and across the river in the densely populated island of Manial Al Rhoda.
Other images showed mounds of debris at the hospital's reception area, mangled and burnt cars in the street outside and a large raging fire with flames shooting into the night sky.
Yet others showed patients, including children, walking away from the hospital after the blast.
A doctor told The National that all 50 patients were moved to nearby hospitals, including those who had been in the intensive care unit.
The hospital remained shut on Monday as experts assessed the structural damage caused by the blast and hospital officials inspected equipment to see if it still worked.
The state-run hospital treats cancer patients from across the country. It is one of several educational hospitals associated with Cairo University's medical school.
There is often a small crowd outside its main entrance, waiting to hear about the condition of relatives and loved ones being treated there.
The hospital is in a busy part of the city with an intricate network of one-way roads and bridges that could be confusing for motorists not familiar with the area.
The road outside the hospital is a key thoroughfare that runs from the heart of the city all the way to the leafy suburb of Maadi and the industrial area of Helwan farther to the south.
The blast occurred about 11.30pm, meaning that traffic policemen normally stationed at intersections had gone home and some motorists may have been speeding.