Hamas was to unveil a new policy document on Monday that eases its stance on Israel after earlier calling for the country's destruction, party officials said.
The announcement was due to be made in the Qatari capital Doha, where exiled Hamas leader Khaled Meshaal is based, at a press conference scheduled for 1745 GMT.
Leaders of the Palestinian Islamist movement have long spoken of the more limited aim of a Palestinian state in the West Bank and the Gaza Strip without explicitly setting it out in its charter.
But after years of internal debate, the party leadership is to publish a supplementary charter that will formally accept the idea of a state in the territories occupied by Israel in the Six-Day War of 1967, a senior Hamas official has said.
The original 1988 charter will, however, not be dropped, just supplemented, and there will be no recognition of Israel, as demanded by the international community, officials have said.
Hamas is considered a terrorist group by Israel, the United States and the European Union, and the new document is aimed in part at easing its international isolation.
The announcement of the new charter was originally scheduled for 1545 GMT but was delayed by two hours because the hotel where the event was to take place backed out of hosting it at the last minute, Hamas said in a statement.
It was also to be broadcast live in the Gaza Strip, the Palestinian enclave run by Hamas.
One Hamas leader, Ahmed Yusef, has told AFP the updated charter was "more moderate, more measured and would help protect us against accusations of racism, anti-Semitism and breaches of international law".
It will "differentiate between Jews as a religious community on the one hand, and the occupation and Zionist entity on the other", he said.
It will also distance itself from the Muslim Brotherhood, to which it was closely linked when formed.
Israel was not convinced, however, with a spokesman for Prime Minister Benjamin Netanyahu saying "Hamas is attempting to fool the world but it will not succeed".
"They dig terror tunnels and have launched thousands upon thousands of missiles at Israeli civilians," David Keyes said in a statement, referring to rockets fired from Gaza and tunnels used to carry out attacks.
Israel and Palestinian militants in the Gaza Strip have fought three wars since 2008.
The strip has been under an Israeli blockade for 10 years.
UN officials have called for this to be lifted, citing deteriorating humanitarian conditions. Israel says it is needed to stop Hamas from obtaining weapons or materials that could be used to make them.
Hamas remains deeply divided from Fatah, the party of Palestinian president Mahmud Abbas based in the occupied West Bank.
Hamas's announcement comes ahead of Abbas's first face-to-face meeting with US President Donald Trump in Washington on Wednesday.
© 2017 AFP