Five years after the Arab League chief Amr Moussa announced that the Middle East peace process was "dead", another blow has befallen the long-vexing struggle between Israel and the Palestinians. George Mitchell, the skilled US diplomat and veteran negotiator, tendered his resignation on Friday, becoming the latest victim in this intractable conflict.

Mr Mitchell leaves without achieving much over his two years of shuttle diplomacy. But this is less an indictment of him than an illustration of the intransigence he has had to confront. Peace may not be dead, but it certainly is on life support.

Mediation requires willing partners. As Mr Mitchell rapidly discovered, that has not always been the case here. Neither side has been willing to enter serious talks, with the Israelis refusing to budge on settlement construction and West Bank land grabs. As the recent Palestinian Papers suggest, the Palestinians have seemed at times to put more on the table, but even they have fallen short.

There is, of course, plenty of blame to go around, and Mr Mitchell's departure is more a symptom of circumstance than a sign of failed strategy. And yet even in this period of renewed uncertainty there is reason for optimism for the weeks ahead.

Fatah and Hamas, long at odds, reached a reconciliation deal last month to form a temporary government. It is hoped that this renewed unity will lend credence to the prospects of official recognition for a Palestinian state, when the UN General Assembly takes up the issue this autumn.

Hamas is still not willing to recognise Israel, and there are doubts about its commitment to peace. But so far the signs are positive; Israel should perceive this unity as a move that will moderate Hamas.

There is no question that Mr Mitchell's departure will leave a void, one that the US president, Barack Obama, should seek to fill immediately. This week Mr Obama will speak to his nation about America's Middle East policy. He is not expected to go into detail on the Israeli-Palestinian conflict, though he should touch on the issue. Silence in the wake of Mr Mitchell's departure would speak volumes. America has long been the only true power broker in this dispute.

Most importantly, though, the US and its Israeli partners should realise that the Palestinians are moving ahead with a state on their own. The outgoing Mr Mitchell understood this. It's time for others to as well.