When the moratorium on Israeli settlement construction in the West Bank expires is somewhat unclear. Some say it ends on September 26; others at the end of the month. What is absolutely clear, however, is that the moratorium must be extended.

There is a small window of opportunity for the Palestinian Authority and the Israeli government to arrive at a two-state solution. It will not remain open forever. Riots on Wednesday after the killing of an Arab resident of East Jerusalem have made this painfully clear. While tensions have eased since, the underlying anger remains. A continuation of settlement construction will stoke it further – perhaps beyond the ability of the Palestinian Authority or its president, Mahmoud Abbas, to control.

In 1947, the United Nations endorsed the creation of Israel, offering it a seat in the community of nations and a place in the international community. But in the six decades since, Israel has yet to understand the obligations of this membership. Rather than follow UN resolutions, it has repeatedly defied them. Nothing has made this more clear than its land grabs in the West Bank since 1967, despite condemnations from the international community and UN rulings on the illegality of settlememts.

Benjamin Netanyahu, like many Israeli prime ministers before him, has said that it is not politically possible for him to end settlement activity. And yet, Mr Netanyahu has never been more popular in Israel. If a leader who has such widespread support cannot find the room to compromise or the ability to make his people aware of its necessity, then who can?

Speaking to the UN General Assembly yesterday the US president, Barack Obama, made the stakes clear: “If an agreement is not reached, Palestinians will never know the pride and dignity that comes with their own state. Israelis will never know the certainty and security that comes with sovereign and stable neighbours who are committed to co-existence.” For this dignity and security to be achieved, and for Mr Obama to make good on the promise of his Cairo address and messages of friendship to the Islamic world, he must act. Mr Obama must find a way to exercise the considerable leverage his nation has over Israel, which it has been too reluctant to employ.

Mr Obama’s secretary of state has referred to one way forward. This week Hillary Clinton praised the Arab Peace Initiative proposed by Saudi Arabia in 2002. Arab states will normalise relations with Israeli in return for Israeli withdrawal from occupied territories and the creation of an independent Palestinian state. This offer may not be on the table forever.

There has never been a better time for Israel to unclench its fist and accept the hand it has been offered. It would be difficult to understand a continuation of settlement activity as anything other than a slap in the face.