Hundreds of followers of firebrand Iraqi Shia cleric Moqtada Sadr demonstrated in Baghdad after Friday prayers, burning Israeli flags.
Worshippers at Baghdad's al-Kazimiyah mosque marched out of the shrine, carrying a symbolic coffin for Yasin, wrapped with a Palestinian flag.
"No, no to Israel. No, no to occupation," shouted the protesters, many carrying portraits of Yasin and Sadr.
When they reached Sadr's nearby offices, a group of youngsters burned two Israeli flags before trampling them.
In the southern Shia city of Najaf, hundreds of worshippers held a similar street protest after Friday prayers at the Imam Ali mosque, following a call for the demonstration by Imam Shaikh Sadreddine al-Qobbanji.
Qobbanji, representative of the Supreme Council of the Islamic Revolution in Iraq (SCIRI) political party in Najaf, asked worshippers to hold the march to honour the "martyrdom" of Shaikh Yasin.
Baghdad erupted in protests
after Friday prayers
In the Iranian capital Tehran, 5,000 Iranians, fired up by a sermon on Yasin's assassination, streamed through the streets on Friday to denounce the Jewish state.
The crowd, composed of women clad in the all-enveloping black chador and bearded men, bellowed "Death to Israel, Death to America" and waved Palestinian flags and posters of Shaikh Yasin.
"Israel is a cancerous tumour that should be cut out," declared one banner. State television reported similar scenes across the Islamic Republic.
Leading conservative cleric Ayat Allah Muhammad Emami Kashani whipped up the crowd with his Friday sermon at Tehran university, telling worshippers: "All independent nations should rise up against this crime."
In the Turkish city Istanbul and capital Ankara, thousands pouring out of mosques in shouted anti-Israeli and anti-US slogans and burned an effigy of Israeli Prime Minister Ariel Sharon.
"All independent nations should rise up against this crime"
Ayat Allah Muhammad Emami Kashani, cleric, Tehran university
Some 2,000 people gathered at Istanbul's Beyazit mosque, one of the city's oldest mosques, and held special prayers in memory of the Palestinian leader, who was killed on Monday by an Israeli missile attack.
Some 300 people, most belonging to a group calling themselves "The Friends of Palestine Initiative," staged a similar demonstration in Ankara, following prayers at the city's historic Haci Bayram mosque.
Turkish Prime Minister Recep Tayyip Erdogan has strongly condemned Yasin's assassination and suggested he would reconsider plans to visit Israel next month.