Abu Fadi, a police officer loyal to Mahmoud Abbas, the Palestinian president, stood up among the roses and lemons in a Gaza garden and pulled down his trousers.

Scars on each knee and ankle and one at his right hip attested to a vicious punishment. He said the wounds were caused by gunmen from Hamas, the Islamic party that rules the sandy coastal enclave and fiercely opposes the Abbas government, which governs the West Bank. The masked men came to his house, told him he was a spy for Israel, shot him nine times from less than a meter away and left him in a pool of blood on his driveway.

“I will have to take revenge,” said Abu Fadi, who asked that his last name not be used. “I can never forgive and forget.” He now walks with crutches because his right leg is paralyzed.

Abu Fadi’s saga reflects the bitter power struggle between Hamas and Mr. Abbas’s Fatah party. The violent conflict is crippling efforts to reconcile the two groups, clouding prospects for possible peace talks with Israel.

At the heart of the dispute is Palestinian discord over future relations with the Jewish state. Unlike Mr. Abbas and Fatah, Hamas refuses to recognize Israel, a requirement of a proposed two-state solution to the Israeli-Palestinian conflict.

Israel initiated a 22-day military assault on the Gaza Strip in December to deter Hamas rocket fire. About 1,300 Palestinians died and 13 Israelis were killed; thousands of homes and scores of public buildings were damaged.

The question of who speaks for Palestinians is a major stumbling block in organizing peace talks with Israel that President Barack Obama has proposed. He is scheduled to address the Muslim world on June 4 in Cairo, where Egypt has been working to bring Hamas and Fatah into a coalition government.

It isn’t clear whether reconciliation will be enough if Hamas, which the U.S. regards as a terrorist organization, refuses to recognize Israel and to commit to the outcome of the negotiations. Prime Minister Benjamin Netanyahu of Israel has yet to agree to the two-state solution.

“It is hard enough to see how peace talks will succeed anyway,” said Mkhaimar Abusada, a political scientist at Al-Azhar University in Gaza. “Maybe we’re headed for a three-state solution: Israel, the West Bank and Gaza.”

Hamas-Abbas antagonism is also contributing to Gaza’s deepening impoverishment. More than $4 billion in Gaza war-reconstruction aid is blocked because international donors, including the United States and the European Union, refuse to give Hamas the money, demanding that Fatah be in charge.

On May 19, the Israeli intelligence chief, Yuval Diskin, told the country’s parliamentary Foreign Affairs and Defense Committee that there could be no peace while Hamas rules Gaza, Israel Army Radio reported. He predicted that the power struggle would continue, with Hamas refusing to relinquish Gaza and Mr. Abbas refusing to give up the West Bank, the radio said.

The internal Palestinian conflict erupted when Hamas swept parliamentary elections in 2006 and reached its height in June 2007, when the Islamic group routed Mr. Abbas’s security forces from Gaza. During Israel’s 22-day offensive last winter, Hamas executed 18 Fatah sympathizers, according to an April 20 report from Human Rights Watch, based in New York. Arrests, torture and killings continued even after the fighting stopped, the report said.

The Palestinian Center for Human Rights, an independent organization, has criticized both sides. In a March 20 report, it took Mr. Abbas’s government to task because “detainees, including children, are subject to torture during interrogation and/or detention.”

“We’re living in an ocean full of grime,” Eyad Sarraj, a physician and human rights activist based in Gaza, said in an interview. “Simply put, this is all criminal activity.”

He estimates that 40 Fatah activists are in Gaza jails and that 400 Hamas supporters are in Fatah detention in the West Bank.

“There is no national mission anymore for the Palestinians, only fighting for power,” said Abu Fadi, 36, who spoke in an isolated compound belonging to his brother on Gaza’s outskirts to avoid being observed talking to a reporter.

He said the Hamas police began to pursue him last year after a bomb exploded near a Gaza beach and killed several Hamas members. The police blamed Fatah and rounded up hundreds of former members of Mr. Abbas’s police force.

Abu Fadi said he wasn’t charged with any wrongdoing; still, Hamas interrogators called him in for questioning during the next few months. He said they suspected he was feeding information on Hamas officials’ movements to Ramallah, Mr. Abbas’s West Bank headquarters. He was beaten, and then on Jan. 20, shot as he sat in front of his home in the Jabalya refugee camp.

Hamas and Fatah officials seek to justify their crackdowns as matters of internal security.

“We have broken up many nests of spies,” said Islam Shahwan, a Hamas police spokesman in Gaza. “They send information to Ramallah, which then passes it to Israel.”

Nonetheless, he said, arrests have been minimal and reports of abuse exaggerated. “What goes on here is nothing compared to the West Bank. There, our people are arrested every day.”

Mr. Shahwan said that during the 22-day war, Fatah militants, including prisoners who escaped from a bombed jail, were shot down by Hamas fighters.

“It was wartime; Israel destroyed our police infrastructure. We could not keep order. We can’t be blamed.”

In Ramallah, Lt. Col. Bilal Abu Hamed, a spokesman for Mr. Abbas’s police force, said that Hamas detainees were put in custody either for arms smuggling or for trying to incite the public against Mr. Abbas and Fatah and that they weren’t tortured.

“It’s nothing like what’s happening in Gaza,” he said. Members of Hamas “think they will go to heaven if they kill someone from Fatah.”

Abu Fadi sees no reconciliation on the horizon.

“Israel takes our land, but Hamas is taking our soul,” he said. “We can’t bargain away our soul.”

Daniel Williams is a columnist with Bloomberg News.