President Miguel Diaz-Canel said the blast at the historic, high-end Hotel Saratoga appeared to have been caused by a gas leak.
Three explosions at a boys' high school in western Kabul also left many injured.
No group immediately claimed responsibility for the blast.
PM Modi invokes the Ahmedabad serial blasts verdict during poll campaign in Uttar Pradesh.
The special court on Friday sentenced 38 convicts to death and 11 others to life imprisonment till death for the Ahmedabad serial blasts, which had claimed 56 lives and left over 200 injured.
On July 26, 2008, Ahmedabad was rocked by a series of bomb blasts planted in 20 places. Nearly 15 years later, the court on Friday awarded death sentences to 38 people and life imprisonment to 11.
Nazeer and the other accused were charged with conspiring, planning and executing the bomb blasts in the KSRTC bus depot and the Mofussil bus stand in Kozhikode on March 3, 2006.
The court allowed the appeal filed by Nazeer and Shafaz against the life imprisonment sentence awarded by the NIA special court.
A Board of inquiry has been ordered to investigate into the cause of this incident.
The blast took place in the wash room of the second floor of the court complex.