Hamas fielded a 3,000-strong militia in Gaza in defiance of Abbas' ban, setting off clashes with Fatah-dominated security forces.

Abbas brought things to a head Thursday, giving Hamas 10 days to achieve a political accord with him or face a referendum within 40 days.

Prime Minister Ismail Haniyeh of Hamas was noncommittal, saying: "We will study how the call for a referendum is compatible with the law, the constitution and politics."

Other Hamas figures were divided over the idea.

Parliament Speaker Abdel Aziz Duaik of Hamas said the prisoners' document was a good basis for dialogue, adding: "Returning to the people is one of the most important principles in democracy."

But Hamas legislator Mushir al-Masri called the proposal a "coup against the democratic choice" of the Palestinians.

The Islamic Jihad group, which also rejects the existence of Israel, opposed the plan.

Israeli Foreign Ministry spokesman Mark Regev called the issue an "internal Palestinian matter," and reiterated that Israel insists on fulfillment of all three international conditions.

Israeli Cabinet minister Haim Ramon, who is close to Prime Minister Ehud Olmert, said the referendum was "worthy of examination." But another Israeli minister, Ronnie Bar-On, said that as long as Hamas does not accept international conditions, Abbas' idea "is like playing checkers with himself."

In Washington, State Department spokesman Sean McCormack said: "The only way you can test the proposition is for the Palestinians to go through that process, whether it's a referendum or whether it's through national dialogue or through some other peaceful means, to talk about what the future of the Palestinian people will be."

Olmert returned Thursday from talks in Washington with President Bush, where he explained his plan to draw Israel's borders unilaterally if efforts to resume peace talks fail. Israel refuses to negotiate with Hamas, which it considers a terror group, and is hesitant to talk peace with Abbas because Hamas controls the government.

However, if Palestinians approve a plan that accepts Israel, Israel might be forced back to the negotiating table.

The Palestinians reject Olmert's unilateral plan, and Abbas' announcement Thursday appeared part of a hurried effort to show the world there is a willing Palestinian partner for negotiations with Israel.

Israeli analyst Yossi Alpher said if a referendum is held and the program is approved, Israel would have to consider it.

"The burden of proof will still be on Abbas to prove that he is a viable negotiating partner," Alpher said.