Three days after Hamas policemen shot and killed at least seven civilians at a rally in Gaza, leading a number of Gazans to express shock and anger at Hamas, Mahmoud Abbas, the Palestinian president and the leader of the rival faction Fatah, called for the ouster of Hamas from power in Gaza.

“We must topple this gang that took control of the Gaza Strip by force and that is exploiting the suffering and tragedies of our people,” Mr. Abbas said in a televised speech on Thursday, delivered from his office in the West Bank city of Ramallah to observe the anniversary of the symbolic November 1988 declaration of a Palestinian state.

Hamas seized control of the Gaza Strip last June after routing Fatah forces in a brief but bloody factional war. Mr. Abbas subsequently fired the Hamas-dominated unity government, in which Fatah had participated, and appointed a caretaker government of moderates in the West Bank. Its authority is not recognized by Hamas.

Mr. Abbas has previously called on Hamas to “reverse the effects of its coup” in Gaza before any national dialogue can be resumed, but this was the first time he had called for its overthrow.

In Gaza, Ismail Haniya, the Hamas leader, responded with a conciliatory speech. He expressed sorrow for the bereaved families, said an investigative committee would be formed and said he had asked for the scores of Fatah members who were arrested after Monday’s rally to be released.

Hamas “is not a bunch of gangs” or “a group that is thirsty for blood,” Mr. Haniya said.

But many here were having second thoughts about life under Hamas’s rule.

Um Ahmed Awouli, 43, a fully veiled mother of five, described herself as a political independent but said she had voted for Hamas in the January 2006 parliamentary elections, which it won.

“Hamas is wrong,” Ms. Awouli said. “Why did they shoot toward the crowd?”

“My son could have been killed,” she added, referring to the rally, which marked the third anniversary of the death of Yasir Arafat, Fatah’s founder and the longtime Palestinian leader. “We voted for Hamas, but now we are angry.”

Some witnesses say that Fatah partly provoked the violence. Soma Abu Aisha, 40, a Fatah supporter who was at the rally, said that what first angered the police was the removal of a Hamas flag from the top of a mosque minaret and its replacement with four Fatah flags. Also, she said that there was “shooting in the air from Al Azhar,” the university affiliated with Fatah, and that “once they shot, Hamas responded, then Fatah shot toward the Islamic University,” which is affiliated with Hamas.

But many Gazans said they were shocked by the reaction of the Hamas policemen, which included the indiscriminate use of live fire to disperse the crowd.

On Wednesday, Amnesty International released a statement condemning the “unwarranted use of lethal force” by the police under Hamas’s control, which resulted in the “unlawful killing” of demonstrators and bystanders, including a child, and the wounding of scores of others.

“I saw them beating children and beating an old woman,” said Aliah Suliman, 30, a teacher who studied at the Islamic University, but who supports Fatah. “They were brutal. They didn’t let an ambulance driver come for those who were bleeding.”

The rally was the largest show of force by Fatah in Gaza since Hamas took over the area. Some came for the love of Mr. Arafat, others because they hated Hamas. But what brought many out was the hardship caused by the economic embargo of the Hamas-ruled strip.

Israel, the United States and the European Union define Hamas as a terrorist organization and say they will have no dealings with it. Since the Fatah forces left their border posts in Gaza, Israel has closed down the main crossings, severely restricting imports into the strip. Only the bare essentials are allowed in. No goods or produce, and hardly any people, are allowed out.

“People are fed up, period,” said Ameer Raghib, 46, a father of five. “That explains the turnout. Now the motor of my refrigerator isn’t working, and I can’t replace it.”

“If there were no siege, Hamas could govern for a hundred years,” he said. “But now people are spitting at Hamas because of the daily suffering.”

Others say the economic situation is not all the fault of Hamas. “We do understand that Hamas has not been given a chance,” said Ms. Awouli, the mother of five. “It’s injustice by the world, and we end up paying the price with our suffocation.”

The best situation, she said, would be for Hamas to be “in charge of resistance,” against the Israelis, “and let Fatah ensure daily life.”

Fatah lost the 2006 elections in large part because of its corrupt image. “Yes, Fatah are a bunch of thieves,” said Ms. Abu Aisha, the Fatah supporter, who was at the rally, “but under them, we lived. I wish for Fatah’s return. The economic situation is disastrous. Now there are no thieves and no life; we are dead.”