Speaking at the Conference of Islamic Scholars in support of Palestine held in Doha, Qatar on Wednesday, Youssuf al-Qaradawi criticised Arab banks for withholding funds from Palestinians.
"If the Arab banks continue to refuse transferring funds to the Palestinian people, we will declare a boycott against them," he said.
The conference was also attended by Khaled Mishal, the Hamas political leader, who called on the Muslim world to send arms, men and money to the Palestinians to fight against the Israeli occupation.
"We ask all the people in surrounding Arab countries, the Muslim world and everyone who wants to support us to send weapons, money and men," Mishaal said.
"You should not shy away from of this. This is resistance, not terrorism," he added.
Hamas, which has largely abided by a ceasefire for more than a year, has been under increasing Western and Israeli financial pressure to recognise the Jewish state, abandon its armed resistance and accept previous Israeli-Palestinian agreements.