Speaking at a rally celebrating the Gaza Strip pullout on Thursday, Hasan Yusif told a 1500-strong crowd in Ram Allah that "no one can deny our right to struggle".
Masked youths could be seen carrying giant models of Qassam rockets, wearing fake explosive belts and holding up posters of the late Shaikh Ahmad Yasin and Abd al-Aziz al-Rantissi, prominent Palestinians assassinated by Israel in 2004.
Although the Israeli government has freed 900 prisoners since Prime Minister Ariel Sharon and Palestinian leader Mahmud Abbas met at an Egypt peace summit in February, more than 7000 still remain behind bars.
Hamas has consistently refused appeals to disarm its resistance militias before taking part in elections in January, when it hopes to make sweeping inroads into the decades-long grip on power maintained by Abbas's governing Fatah party.
Under huge pressure from Israel and the international community, Abbas has promised to step up the Palestinian security presence in the West Bank and Gaza Strip following very public shows of strength by armed resistance groups.
At talks with Hamas and the other main Palestinian factions on Wednesday, Abbas persuaded them to end all armed rallies celebrating the end of 38 years of Israeli military rule in the Gaza Strip.