The marches reflected the growing anger over the mounting civilian casualty toll and suffering from the Israel-Hamas war.
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In Jerusalem on Saturday protesters demanded more action from the Israeli government to release around 240 hostages held by Hamas in Gaza.
Some wanted the war to stop, saying peace is the only solution.
In Iran mass protests were organised by the authorities against Israel's invasion of Gaza.
Iran is fiercely opposed to Israel's existence and helps fund the Shiite Muslim militant group Hezbollah in Lebanon which has been attacking Israel with Iranian supplied missiles since the war began.
In Ireland protesters demanded a ceasefire. Unlike many western European countries Ireland's governments have frequently criticised Israel, whilst at the same time supporting Palestinian rights.
Protests calling for a ceasefire were also been held in many capitals in Europe on Saturday including Paris.
Protesters, particularly in countries with large Muslim populations, including the U.S., U.K. and France, have for weeks expressed disillusionment with their governments for supporting Israel while its bombardments of hospitals and residential areas in the Gaza strip intensify.
More than 12,300 Palestinian men, women and children have been killed so far, according to the Hamas run health ministry.