Gaza rulers Hamas have called for unity among Palestinians and "resistance" against Israeli plans to annex parts of the occupied West Bank.
Israeli Prime Minister Benjamin Netanyahu aims to begin a process of annexing West Bank settlements and the Jordan Valley from 1 July, as part of a US peace initiative.
"We call for the annexation project to be confronted with resistance in all forms," said senior Hamas official Salah al-Bardawil.
"We call on our people to transform this hardship into an opportunity to get the Palestinian project back on track," he told a press conference.
Hours later the Israeli army said that a rocket had been fired from the Hamas-ruled Gaza Strip "into Israel", the first such act in more than a month. It gave no further details.
Deep divisions remain between Islamist movement Hamas and the Palestinian Authority, based in the West Bank city of Ramallah, but Bardawil called for a "union of the political class".
"It is the duty of each free Palestinian citizen to rise up against this flagrant aggression on our land," he said.
Mr Bardawil called for a meeting between Hamas and the Palestine Liberation Organisation, which includes various other Palestinian groups.
Hamas took control of Gaza in 2007, after ousting forces of president Mahmoud Abbas in a near civil war among the Palestinians.
Both the PA and Hamas stand opposed to annexation in the West Bank, which forms part of a controversial peace plan unveiled in January by US President Donald Trump.
The initiative paves the way for the eventual creation of a Palestinian state, but on reduced territory and without key Palestinian demands such as a capital in east Jerusalem.
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.
