The Fatah movement of the Palestinian Authority President, Mahmoud Abbas, has refused to join a government being formed by Hamas.
Fatah spokesman Azzam al-Ahmad said weeks of talks on Hamas' political programme had failed.
Fatah, which lost elections in January, had wanted Hamas to recognise previous Palestinian agreements with Israel.
Hamas leaders said this would mean accepting the Israeli occupation of Palestinian land.
Hamas is expected to present its list of ministers to Mr Abbas on Saturday.
The militant group won 74 seats of the 132 contested in the Palestinian Legislative Council elections in January.
'Greater challenge'
Fatah is the party founded by Yasser Arafat and has dominated Palestinian politics for decades.
BBC Gaza correspondent Alan Johnston says a Hamas-led government without Fatah may make the task of governing an even tougher challenge for the militant group.
Fatah ministers might have taken on responsibilities for dealing with Israel and the West.
The Israelis, the Europeans and the Americans all regard Hamas as a terrorist organisation, and the EU and the US are talking of cutting crucial flows of aid funding if a Hamas-led government refuses to lay down its arms and pursue peace with Israel.
At the same time, our correspondent says, there are many areas of Palestinian life that Hamas regards as being in desperate need of reform.
Carrying out some of that restructuring process might have been a little easier if Fatah were inside the government and co-operating with its programme.