The protest — the latest large-scale rally of its kind in the North African nation — was called by Al Adl Wal Ihssane, an Islamist group that is banned but tolerated.
The group also organized similar gatherings in the capital Rabat and the port of Tangier.
The demonstrations were held to mark the last Friday in the holy fasting month of Ramadan, and Quds (Jerusalem) Day when annual rallies in support of the Palestinians are held around the region.
"Normalization is a hoax!" and "Down with the occupation!," protesters chanted in Casablanca, with the war between Israel and the Palestinian militant group Hamas about to enter its seventh month.
In late 2020, Morocco established diplomatic ties with Israel under the United States-brokered Abraham Accords which saw similar moves by the United Arab Emirates and Bahrain.
As part of the deal, Rabat received Washington's recognition of its claim to sovereignty over the disputed territory of Western Sahara.
Since the Israel-Hamas war in Gaza began on October 7, large-scale demonstrations in the North African kingdom have called for the abrogation of the normalization deal.
"We came to say 'no' to the barbaric massacres Israel is committing against Palestinians, to the destruction in Gaza... and to the silence of the Arab states," protest organizer Mohammed Riahi told AFP.
Casablanca lawyer Mohammed Ennouini, 51, said: "Normalizing ties between Arab states and Israel gives it the green light to keep killing civilians."
Rabat has officially denounced what it said were "flagrant violations of the provisions of international law" by Israel in its war against Hamas, but has not given any indication that normalization with Israel would be undone.
According to the health ministry in the Hamas-run Gaza Strip, at least 33,091 people have been killed in the territory during the war.
It began after Hamas's October 7 attack which left 1,170 people, mostly civilians, dead in southern Israel, according to an AFP tally of Israeli official figures.
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