Carrying Palestinian flags, banners and posters, some of them plastered with the pictures of Shaikh Ahmed Yasin, the slain leader of Hamas, the protesters chanted anti-Israel slogans.
In Karachi, thousands took part in a car rally that culminated at the Karachi Press Club after passing through key city roads.
Several cars were decorated with Palestinian flags, while angry protesters also burned Israeli flags.
Addressing the rallies, the political and religious leaders regretted the mere "lip servicing" by Muslim leaders, mainly the Arab world and the Organization of Islamic Countries against Israeli atrocities.
This continuing inaction, they said, has encouraged the Zionist state to evict Palestinians from their lands.
Meanwhile, the government of southwestern Balochistan province announced to observe Day of Solidarity with Palestinians on Monday to honor Palestinian martyrs and condemn Israel's aggression.
The tensions that began in Ramadan in East Jerusalem spread to Gaza after Palestinian resistance groups there vowed to retaliate against Israeli assaults on the Al-Aqsa Mosque and Sheikh Jarrah neighborhood.
