Several Palestinian civilians, including three children, died from shellfire as they were picnicking on a northern Gaza beach on Friday.
Palestinians said the beach, near Beit Lahiya, was hit by Israeli shells.
At least 30 people were injured, with many rushed to hospital for treatment.
Israel launched an inquiry into whether its artillery or gunboats were responsible.
Thousands crammed the streets of Rafah earlier for the funeral of Jamal Abu Samhadana, a senior militant killed by air strike on Thursday.
The body of the founder of the Popular Resistance Committees was carried through the heat and dust for his burial.