If few expected the speed and skill of Egypt's diplomatic corps as it navigated Wednesday's deal between Hamas and the Palestinian Authority, the response from Israel was all too predictable.

"The Palestinian Authority has to decide on having peace with Israel or peace with Hamas," the Israeli prime minister, Benjamin Netanyahu, declared in response to the preliminary accord inked in Cairo. "You can't have peace with both."

It is a statement that is both absurd and disingenuous. Absurd, because no lasting peace with the Palestinians can exclude Hamas and its supporters. If only a fraction of the Palestinian leadership strikes a deal with Israel, it is not a two-state solution, but an agreement to be co-opted. Mr Netanyahu's government has consistently driven a wedge between Palestinian factions with just this goal in mind.

The prime minister is doubly disingenuous because his administration has consistently blocked even a partial peace deal. Before talks stalled last year, the Palestinian Authority had offered everything it could - more than it should have - to no avail. Professing a belief in a two-state solution, Israel's government at the same time built every roadblock to its realisation.

If Palestinian leaders on both sides can hold to their word and this unity deal moves forward, they will have stripped Israel of its pretence. The refusal to negotiate with Hamas is an old line, an attempt to portray the entire party, which won the 2006 elections, as intractable enemies and its supporters as terrorists.

Elements of Hamas that remain committed to violence will be a test of this unity accord, not to mention the party's own viability, but Israel's assertions are demonstrably false. It sets the precondition to negotiations that Hamas recognise Israel's right to exist; the party officially refuses to do so, but before the stranglehold blockade of the Gaza Strip, its political leader Khalid Meshaal had offered Israel a 10-year truce. "The problem is not that there is an entity called Israel," Mr Meshaal told Reuters in 1997. "The problem is that the Palestinian state is non-existent."

Only if Hamas stands separate from the Palestinian Authority, the "legitimate" Palestinians, can Israel pretend it wants peace while it is working against it. Israel's allies in Washington must also realise this self-deception serves no one.

Wednesday's deal in Cairo is still a fragile enterprise that either Fatah or Hamas could torpedo with a word. It is also the only way forward towards a unified Palestinian state. When Israel realises that this is in its interests, there will be a chance for peace.