killing 15 at the border fence.
As many as 30,000 arrived early in the day at tent encampments on Gaza’s side of the fence to stage what was billed as the start of a peaceful, six-week sit-in. They were protesting against Israel’s longstanding blockade of the territory and in support of their claims to return to homes in what is now Israel.
But as some began hurling stones, tossing Molotov cocktails and rolling burning tires at the fence, the Israelis responded with tear gas and gunfire. The Israelis said they also exchanged fire with two gunmen across the fence and fired at two others who tried to infiltrate into Israel.
Mohammad Obaid, an 18-year-old protester, said that holding a Palestinian flag in one hand and a rock in the other would be enough to get him killed by an Israeli soldier.
“We can bring back our lands with the power of guns and weapons, not with a march, a stone or a knife,” he said after the violence erupted.
Friday’s flare-up, ignited by isolation and economic deprivation, was the worst in years in the small Mediterranean enclave. In recent years, neighboring Egypt has joined Israel in the blockade, and the Palestinian Authority, which administers the West Bank, has imposed sanctions. With the territory’s economy collapsing, fears of an explosive backlash have mounted.
In December, some Palestinian leaders had called for mass protests when the United States declared Jerusalem the capital of Israel and said it planned to move the American Embassy there. Such demonstrations never materialized.
The Palestinian organizers of the protest bused men, women and children to tent encampments that popped up in recent days about 700 yards from the border with Israel. They intended for the six-week campaign to culminate in a mass march toward Israel, putting Israeli officials on edge.
Even before the protests started, Israel began a campaign to hold the Islamic militant group Hamas, which controls Gaza, responsible for any violence. The country’s hard-line defense minister, Avigdor Lieberman, warned Gazans to keep away from the border in a post on Twitter in Arabic.
“The Hamas leadership is risking your lives,” he wrote. “I advise you to get on with your normal everyday lives and not to participate in the provocation.”’
Those tensions were also fed in recent weeks by Palestinian militants planting explosives along the border, with some cutting through the fence. Armed with knives and grenades, they set fire to Israeli military equipment — apparently testing Israeli preparedness and worrying local communities.
Israel had almost doubled its forces along the border, deploying snipers, special units and drones, and warning that it would act to prevent any breach of the border fence. B’Tselem, an Israeli human rights organization, had warned that any shoot-to-kill policy against unarmed demonstrators would be illegal unless soldiers’ lives were threatened.
Most of the protesters in the tent encampments remained well away from the border fence and did not participate in the violence.
After the violence began, the Israelis declared the area surrounding Gaza a closed military zone, and said they had responded with riot-control methods and had fired toward the “main instigators.” The Palestinian Health Ministry in Gaza put the number of deaths at 15; the Israeli military said it was not able to verify the number.
The idea for border encampments was initiated by a Gazan social-media activist, Ahmed Abu Artema, a political independent. It was quickly adopted by Hamas, which promoted the protest on its social media platforms and urged Palestinians to participate.
“Our will in achieving the actual return to our lands is more powerful than jet fighters and a gun,” Mr. Abu Artema said by phone on Friday as he was on his way to the protest. “This march is rightful and will not be used and exploited for political agendas.”
Before the main confrontation broke out, the Palestinian Health Ministry reported that a Palestinian man, a farmer, was killed near the border zone early Friday by Israeli artillery fire — one of the 15 it reported dead later in the day, along with some 1,000 injured. The Israeli military’s account said one of its tanks had fired on two Palestinians who approached the border and were “acting suspiciously.”
“We are raising the flags of peace and have nothing to harm the enemy,” said Hamed Jundiya, 63, an educational supervisor who erected his tent a few hundred yards from the border fence. Gazans are desperate, he said, “living without work, electricity and open borders.”
The peak of the Gaza protest was supposed to take place on May 15, when Palestinians commemorate what they call the Nakba, or catastrophe, the anniversary of Israel’s declaration of independence and the 1948 war in which hundreds of thousands of Palestinians lost their homes through flight and expulsion.
This year, May 15 is expected to be particularly sensitive. It comes a day after the expected move of the United States Embassy to Jerusalem from Tel Aviv, a step that has provoked international criticism and Palestinian outrage. It also coincides with the start of Ramadan, the Muslim holy fasting month.
Organizers of the border protest had hoped to create an almost festival-like atmosphere to attract families, setting up portable washrooms and providing free food, water and Wi-Fi. But tensions in Gaza had been building for weeks.
Friday’s protest also fed on Palestinian anger over the failing reconciliation process between Hamas and Fatah, the rival, mainstream movement led by Mahmoud Abbas, whose Western-backed Palestinian Authority holds sway in parts of the West Bank.
Mr. Abbas, whose forces were routed from Gaza during factional violence in 2007, has vowed to tighten economic sanctions on the enclave, where most of the population lives in poverty and lacks such basics as regular electricity.
Mr. Abbas declared a national day of mourning on Saturday.
Israel has fought three wars in Gaza over the past decade and has invested heavily in combating the threat posed by rockets fired by Hamas and other militant groups, and from tunnels crossing under the border.
Isabel Kershner reported from Jerusalem, and Iyad Abuheweila from Gaza. Ibrahim El-Mughraby contributed reporting from Gaza.