Hamas has called for unity among Palestinians and "resistance" against Israeli plans to annex parts of the occupied West Bank.
Senior Hamas official Salah al-Bardawil said at a news conference in the besieged Gaza Strip on Monday: "Palestinian unity is the bedrock of national strength through which the [planned catastrophic] annexation can be resisted and foiled."More: Interactive - Israel's settlements: More than 50 years of land theft explained The architects behind the US plan Trump's US-Israeli plan announcement: Why now?
He called for popular Palestinian actions against planned annexations, such as demonstrations.
"It is the duty of each free Palestinian citizen to rise up against this flagrant aggression on our land," he said.
Deep divisions remain between Hamas, which governs Gaza, and the Palestinian Authority (PA) based in the West Bank city of Ramallah, but Bardawil urged a "union of the political leadership".
He called for a general meeting between Hamas and the Palestine Liberation Organization (PLO), which includes various other Palestinian groups.
Hamas took control of Gaza in 2007, after defeating forces loyal to Palestinian President Mahmoud Abbas in a near civil war after Hamas won elections in 2006.
Both the PA and Hamas stand opposed to annexation in the West Bank, which forms part of a plan by US President Donald Trump.
Unveiled in late January, Trump's plan proposed the establishment of a demilitarized Palestinian state on the remaining patchwork of disjointed parts of the Palestinian territories without occupied East Jerusalem, which Palestinians want as the capital of their future state.
The planned Israeli annexation would deprive Palestinians of key agricultural land and water resources, especially in the Jordan Valley region. It would also effectively kill the two-state solution to the Arab-Israeli conflict that was based on the idea of land for peace.
Israel's intention to press ahead with annexation has been met with warnings from the United Nations that such a move would likely spark violence.
Israeli Prime Minister Benjamin Netanyahu has said his government aims to begin the process of annexation of West Bank settlements and the Jordan Valley from July 1.
Israel occupied the West Bank, East Jerusalem, Gaza and the Syrian Golan Heights after capturing the territories during the 1967 war. Israel annexed East Jerusalem and the Syrian Golan heights in 1980 and 1981 respectively, although the moves were not recognised by the vast majority of the international community.
Last week, hundreds of international law professors and scholars signed an open letter condemning the Israeli plans to annex territory in the West Bank, calling it a "flagrant violation of bedrock rules of international law, and would also pose a serious threat to international stability in a volatile region".
Kevin Jon Heller, an international law professor, told Al Jazeera the Israeli planned annexation is a "clear and fundamental violation of international law that prohibits annexation of territories taken by force".
"Israeli annexation of the Golan Heights and Jerusalem coupled with international and Arab silence have emboldened it to take further action in that direction as its contemplating now," said Heller.