"No one can disarm the resistance," Mashaal said in a televised speech from Doha on Wednesday.
Twenty-eight foreign ministers of EU member states had on Tuesday called on Hamas' al-Qassam Brigades and other resistance groups to disarm.
Mashaal's speech came as the death toll from Israel's latest assault on Gaza neared 700 on the 16th day of the offensive. Over 4,000 Palestinians have been wounded and some 140,000 have been displaced due to the Israeli attacks.
"We cannot accept any proposal that does not include the lifting of the siege on Gazans," Meshaal said.
"How many Israeli soldiers is Israel willing to see dead before the siege is lifted?"
Some 31 Israeli troopers have been killed by Palestinian fighters since the military began a mass ground invasion on July 17, according to the Israeli regime’s figures. Hamas , however, said that Palestinian resistance fighters have killed over 40 Israeli troops since Tel Aviv started its offensive on the besieged Gaza Strip.
The leader bemoaned the severe number of Palestinian casualties and the breakdown of the humanitarian situation in Gaza since the start of the offensive.
"Everything in Gaza is collapsing," Mashaal said. "No water, no electricity, no medicine, no fuel, no food."
He urged UN chief Ban Ki-Moon to visit Gaza to witness the effects of the onslaught firsthand.
The Gaza Strip has been under a severe economic blockade imposed by Israel since 2006.
The blockade has severely limited the imports and exports of the Gaza Strip and has led to frequent humanitarian crises and hardship for Gazans.
NTJ/NJF