Palestinian authorities said a grave site discovered at the Nasser hospital, the main medical facility in central Gaza, contained nearly 400 bodies
Hundreds of people have died in Islamist violence over the past months and more than 150,000 have been forced to flee as jihadist groups spreads across the arid Sahel region.
Once a pocket of calm in the Sahel, Burkina has suffered a spillover of Islamist violence from neighbouring Mali, where an attack on a village on Sunday left at least 95 dead and more than a dozen missing.
Deteriorating security prompted the government to declare a state of emergency in several northern provinces bordering Mali in December, which was extended by six months after jihadists attacked civilians in Arbinda's Soum province.
Burkina's armed forces have launched a search operation across the area targeted by Sunday's attack, the government said late on Monday.