Speaking in Gaza City, Mahmoud al-Zahar, a regular critic of Israel, said the political policy document announced in Qatar on May 1 by Hamas's outgoing chief Khaled Mashaal did not contradict its founding covenant, published in 1988.
Trailed for weeks by Hamas officials, the document appeared to be an attempt to soften the group's language towards Israel. But it still called for "the liberation of all of historical Palestine," said armed resistance was a means to achieve that goal, and did not recognize Israel's right to exist.
"The pledge Hamas made before God was to liberate all of Palestine," Zahar said on Wednesday. "The charter is the core of (Hamas's) position and the mechanism of this position is the document."
Many Western countries classify Hamas as a terrorist group over its failure to renounce violence, recognize Israel's right to exist, and accept existing interim Israeli-Palestinian peace agreements.
In its new document, Hamas said it agrees to a transitional Palestinian state within frontiers pre-dating the 1967 Six-Day War but continues to oppose recognizing Israel's right to exist and backs an armed struggle.
Western-backed Palestinian President Mahmoud Abbas, who heads the rival Fatah movement that controls the West Bank, claims to recognize Israel and seeks a final peace agreement based on those lines.
US President Donald Trump will meet Abbas and Israeli Prime Minister Benjamin Netanyahu when he visits the region later this month, and a summit to restart peace talks stalled since 2014 has been mentioned in media reports.
Zahar denied that Hamas was trying to align itself with Fatah's position.
"When people say that Hamas has accepted the 1967 borders, like others, it is an offence to us," he said.
"We have reaffirmed the unchanging constant principles that we do not recognize Israel; we do not recognize the land occupied in 1948 as belonging to Israel and we do not recognize that the people who came here (Jews) own this land.
"Therefore, there is no contradiction between what we said in the document and the pledge we have made to God in our (original) charter," Zahar added.