Gaza Strip — Large crowds of flag-waving Palestinian protesters marched toward the Gaza border fence with Israel on Friday, some of them throwing stones and drawing Israeli fire that officials said killed at least six people.It was the deadliest day in Gaza in several months.The Palestinian Health Ministry said at least 550 Palestinians were hurt by live fire, rubber-coated steel pellets or tear gas fired by Israeli forces at several locations along the fence, but did not provide the breakdown.The protests marked the launch of what Gaza's Hamas rulers envision as a 6-week-long campaign of mass sit-ins along the border, meant to spotlight the demand of uprooted Palestinians and their descendants to return to what is now Israel. It's also seen as a new attempt by Hamas to break a decade-old Gaza border blockade.On Friday, protests quickly spun out of control.Israel's military said thousands of Palestinians rolled burning tires and threw stones at forces stationed on the border, and that troops opened fire at the "main instigators."Palestinian witnesses said tens of thousands gathered in tent encampments set up at five sites at a distance of several hundred meters (yards) from the border, but that only some of them engaged in clashes.Such mass gatherings near the border signal a new tactic by Hamas — and one that might prove more challenging to Israel's military than previous smaller protests.Military officials have said they will respond harshly to any breaches of the border fence. At the same time, a rising number of casualties will likely stoke more border tensions, a scenario Israel hopes to avoid.The sit-ins are seen as a new attempt by Hamas to break a crippling, decade-old Gaza border blockade by Israel and Egypt that has made it increasingly difficult for the Islamic militant group to govern.Other tactics over the years, including Hamas' cross-border wars with Israel and attempts to reconcile with political rival Mahmoud Abbas, the West Bank-based Palestinian president, have failed to end Gaza's isolation.Hamas spokesman Fawzi Barhoum praised the turnout."The large crowds ... reflect the Palestinian people's determination to achieve the right of return and break the siege and no force can stop this right," he said.Friday's actions are to be the first in a series of protests planned in Gaza in coming weeks. The protests are to culminate on May 15, the 70th anniversary of Israel's creation, with a march through the border fence.Palestinians commemorate the date as the anniversary of their mass displacement and uprooting during the 1948 Mideast war over Israel's creation. The vast majority of Gaza residents are descendants of Palestinians who fled or were driven from communities in what is now Israel.Israel's military said ahead of Friday's protests that it doubled its standard troop level along the border, deploying snipers, special forces and paramilitary border police units, which specialize in riot control.Maj. Gen. Eyal Zamir, commander of the Israeli military's Southern Command, which includes the border, said Friday that "we are identifying attempts to carry out terror attacks under the camouflage of riots."He urged Gaza residents to stay away from the border, and held Hamas responsible for any violence there.Previous protests near the border fence in recent months have turned deadly, with Israeli soldiers firing live bullets at Palestinians burning tires, throwing stones or hurling firebombs.On Friday, buses took protesters to the border area, including five tent encampments set up from north to south, several hundred meters from the border fence. By noon, thousands had arrived at the encampments.At one encampment, east of Gaza City, people clustered around the tents. An unpaved road linking the tents and the border fence was filled with people walking in both directions. People ran for cover from time to time to escape tear gas.Ghanem Abdelal, 50, distributed water bottles to family members sitting on a mat near one of the tents. He said he hopes the protest "will bring a breakthrough, an improvement, to our life in Gaza."Ismail Haniyeh, Hamas' supreme leader, visited the tents, along with Gaza leader Yehiyeh Sinwar.The Palestinian Health Ministry said six people were killed by Israeli fire in border clashes, including a 16-year-old boy and a 33-year-old man.Earlier Friday, in a separate incident, a Palestinian farmer identified as 27-year-old Amr Samour was killed by an Israeli tank shell while he was working in his field before dawn in southern Gaza, the ministry said.Israel said troops had directed tank fire at suspicious figures near the border fence in the area.Yasser Samour, a relative and fellow farmer, said Amr Samour was harvesting parsley before dawn, in hopes of selling it fresh in the market later in the day."I was working on the next field," Yasser Samour said. "We heard shelling landing on the field where Amr works. We ran there and found him hit directly with a shell. We were more than a kilometer away from the border."Another farmer was wounded in the leg by shrapnel, Samour said.