Leading Moroccan officials, government and opposition politicians joined the Casablanca street march which also brought together trade unions and rights groups.
Abderrahim Boualem, 55, who worked as a driver, and 49-year-old maintenance employee Abderlkrim al-Mouhafidi, were captured on October 20.
They had been returning to the Moroccan embassy in Baghdad after collecting their salaries from Morocco’s mission in Jordan when they were taken, according to a report by the Moroccan Times newspaper.
Six days later, the Iraqi wing of al-Qaeda, led by Abu Mussab al-Zarqawi, issued a statement saying the two Moroccans had been sentenced to death after a “sharia court … decided that they were without a doubt loyalists of the oppressors and elements of the apostate regime in Morocco.”
The Moroccan foreign ministry has vowed it will not succumb to “blackmail”, particularly “coming from a terrorist group which cannot claim to represent Iraq.”
The ministry has also demanded “the immediate and unconditional release” of the captives, saying that al-Qaeda had used “so-called religious references and fallacious political ideas” to justify its threat of a “cowardly execution” of the pair.
Among yesterday’s 10,000 Casablanca protesters was Chakib al-Mouhafidi, the brother of one of the hostages.
“We cannot describe our feelings after this demonstration. All participants are Abdelkrim, they are one voice,” Mr Mouhafidi told the Reuters news service.
Other marchers held aloft banners and chanted: “Muslims are brothers. A Muslim does not kill his brother” and “’Yes’ to freedom, ‘No’ to terrorism and barbarity.”
Zarqawi’s group has previously claimed responsibility for the abduction and killing in July of two Algerian diplomats and the head of Egypt’s mission in Baghdad, Ihab al-Sherif.