The crowd departed from Nablus' Old City al-Nasir Mosque on Friday and marched towards the centre of town.
The marchers waived Hamas' trademark green flag and chanted "We will sacrifice our soul and our blood for you Sheikh Yasin!" and "For every threat to Sheikh Yasin, Israel will pay a high price."
Israel believes Yasin, who escaped an attempt on his life last year, personally ordered a deadly human bombing at a border crossing with Gaza last week which prompted Deputy Defense Minister Zeev Boim to mark him for death.
Target for assassination
On Monday, Israeli army chief General Moshe Yaalon also said
Yasin was a target for assassination. "For us, Sheikh Yasin is a target for liquidation, given that there is no distinction to be made between the political and military leadership of Hamas," he said.
Yasin, who founded Hamas in 1987, has refused a truce with
Israel unless the Jewish state stops its policy of assassinating
leaders of armed fighters and its deadly invasions of the Palestinian territories.
Hamas, along with all major armed groups, unilaterally froze its anti-Israeli attacks last June but the truce held out for a mere seven weeks.