Hamas Prime Minister Ismail Haniyeh slammed the Obama administration's plan to meet Tuesday with Israeli Prime Minister Benjamin Netanyahu and Palestinian President Mahmoud Abbas, saying that Palestinians will reject anything Mr. Abbas agrees to during discussions on the sidelines of the United Nations General Assembly in New York.

His comments come one day after militants in Gaza fired two rockets into Israel and as a flare up in violence along the Gaza border left two militants dead.

"Any signature will be invalid, and it won't bind the Palestinian people to anything," Mr. Haniyeh said in a sermon in Gaza City at the start of the Muslim Eid al-Fitr holiday. "No one has the right to give up on Jerusalem or the [Palestinian] refugees. Not the [Palestine Liberation Organization] nor any other faction can sign an agreement hurting the Palestinian people's principles and rights."

For Palestinians, Haniyeh's remarks were a jab at his rival, Mr. Abbas, for relenting on a demand that Israel agree to a freeze in settlement construction as a condition to resuming talks with Mr. Netanyahu. And the timing of his comments serve as a reminder that Hamas, which maintains control of Gaza, could play spoiler to this week's attempt to get peace talks back on track.

The about-face "embarrasses the Palestinian leadership," says Ghassan Khatib, a former Palestinian cabinet minister. "This meeting weakens the position of [Abbas] and it makes sense [for] his opponent to take advantage of it."

A spokesman for Abbas's Palestinian Authority insisted that the meeting in New York would not mark the beginning of negotiations, according to media reports. But even the act of meeting with Netanyahu and Obama before Israel imposes a complete freeze on the contruction of settlements is deeply unpopular in the Palestinian territories.

Mitchell so far falls short

US envoy George Mitchell has so far fallen short of an agreement with Israel on US demands for a settlement freeze, which the US sees as a key springboard to negotiations. Israel has been hoping to get an Arab quid pro quo on normalizing ties.

In Israel, the daily Ha'aretz reported that that Israeli and US officials also said that the three-way meeting would not mark the resumption of talks. But that may do little to allay Arab concerns that Abbas is capitulating.

Abbas's improved standing

Abbas's standing among the Palestinian public has improved in recent months because of beefed up security in West Bank cities, an economic revival, and refusing to return to talks with Israel. Hamas, meanwhile, has been struggling in a coastal enclave economically devastated by Israel's blockade and physically destroyed by the Jewish state's January offensive to stop rocket fire.

According to an August public opinion survey by pollster Khalil Shikaki, Abbas tripled his advantage over Haniyeh to 14 percentage points. At the same time, Abbas's Fatah party doubled its lead over Hamas to 16 percentage points.

Palestinian pessimism

But Palestinians are increasingly pessimistic about the prospects of Hamas and Abbas reconcilining any time soon. In the Shikaki poll, only 12 percent said they expected a reunification of the West Bank and Gaza soon.

Hannah Sinora, the co-director of the Israel Palestinian Center for Research and Information, says that Hamas's reflexive rejection of peace talks before they are even started reflects confusion among the Islamic militant leadership in Gaza. Though Hamas control over Gaza is tight, Mr. Sinora says that Gazans are grumbling about their leaders.

"Hamas is trying to jump the gun and say they are against any type of settlement," he said. "That means that deep down that they fear that they have lost the support of the Palestinian people."

Haniyeh declared in his sermon that Hamas hasn't abandoned the its original principles – which favor armed attacks on Israeli targets. The group is considered a terrorist organization, according to the US

Hamas has been the main critic of the peace talks backed by Abbas, arguing that 15 years of negotiations have gotten the Palestinians no closer to statehood. According to the conventional wisdom of peace proponents, a successful conclusion to peace negotiations would further marginalize Hamas.

Hamas, the spoiler?

After winning a parliamentary election in 2006 and overrunning Gaza the next year, the Islamic militants strengthened their leverage to be a potential spoiler for any successful conclusion of peace talks.

A Hamas gunman and another militant from a related Gaza militia were killed on Sunday by Israeli fire aimed at militants near the border fence with Israel, news reports said. Overnight Saturday, Gazan militants fired two rockets in the direction of southern Israel, though no one was injured.

"Hamas is trying to appear now as if they are the only authorized power in the Palestinian land," says Nashat Aqtash, a lecturer in communications at Bir Zeit University. "His message for the Israelis and the Americans is: Remember that if you sign an agreement it has no meaning. We are the only legitimate power. You have to talk to us."