Palestinians marked a general strike and a day of mourning on Saturday over the death of 15 Palestinians by Israeli gunfire during rallies demanding the right of return to refugees.
Shops across the occupied West Bank shuttered their doors, universities and schools suspended their classes and most businesses observed the general strike.
At least 15 Palestinians from the Gaza Strip were martyred and hundreds injured when Israeli forces opened fire on protesters marking "Land Day", an annual Palestinian commemoration of the deaths of six Arab citizens of Israel killed by Israeli forces in 1976 during demonstrations over government land confiscations in northern Israel.
Palestinian President Mahmoud Abbas declared Saturday a day of mourning over Friday's deaths.
"Palestinian factions have responded to the president's decision to declare mourning for the victims of the Israeli massacre," Wasel Abu Yusuf, a member of the Palestine Liberation Organization (PLO)'s executive committee, told Anadolu Agency.
"The national and Islamic forces declared a general strike in all Palestinian areas and called for demonstrations to protest the Israeli massacre against our people in Gaza," he said.
Friday's rallies were the start of a six-week protest that culminates on May 15, the day the Palestinians call as "Nakba", or "Catastrophe", when Israel was created.
The demonstrators are demanding that Palestinian refugees be allowed the right of return to towns and villages which their families fled from, or were driven out of, when the state of Israel was created in 1948. Hundreds of thousands were uprooted during the 1948 war over Israel's creation and the vast majority of Gaza's 2 million people are descendants of Palestinians who fled or were driven from homes in what is now Israel.
Meanwhile Israel will target "terror organizations" in Gaza if violence along the territory's border with Israel drags on, the chief military spokesman warned Saturday, despite international calls to restrain use of force against civilians.
In Friday's confrontations, large crowds gathered near the border fence, with smaller groups of protesters rushing forward, throwing stones and burning tires. Israeli troops responded with live fire and rubber-coated steel pellets, while drones dropped tear gas from above. The army released video showing soldiers with rifles perched on high earthen embankments overlooking the scene.
Brig. Gen. Ronen Manelis, the chief army spokesman, denied allegations of excessive use of force, saying those killed by Israeli troops were men between the ages of 18 and 30 who were involved in violence and belonged to militant factions.
He alleged Gaza health officials exaggerated the number of those wounded, and that several dozen at most were injured by live fire while the rest were merely shaken up by tear gas and other riot dispersal means.
Gaza City's Shifa Hospital received 284 injured people Friday, the majority with bullet injuries, said spokesman Ayman Sahbani. He said 70 were under the age of 18 and 11 were women.
He said 40 surgeries were performed Friday and that 50 were planned Saturday. "These are all from live bullets that broke limbs or caused deep, open wounds with damage to nerves and veins," he said.
Among those recovering from surgery was 16-year-old Marwan Yassin who had thrown stones with a slingshot at the fence Friday and was shot in both legs. One of his legs was wrapped in bandages and the other had a cast and metal fixtures.
His mother said at his bedside that she would ban him from future protests.
On Saturday, a few hundred people gathered at five tent encampments that have been set up several hundred meters from the border fence. The tents serve as the launch points for marches.
Protest organizers have said mass marches would continue until May 15, the 70th anniversary of Israel's creation.
Manelis reiterated Saturday that Israel "will not allow a massive breach of the fence into Israeli territory."
He claimed that Hamas and other Gaza militant groups are using protests as a cover for staging attacks. If violence continues, "we will not be able to continue limiting our activity to the fence area and will act against these terror organizations in other places too," he said.
The border protests were seen as a new attempt by Hamas to break the border blockade, imposed by Israel and Egypt after the group seized Gaza from forces loyal to its rival, Palestinian President Mahmoud Abbas, in 2007. The continued closure has made it increasingly difficult for Hamas to govern.
The large turnout of marchers in the dangerous border zone also seemed to signal desperation among Gaza residents. Life in the coastal strip has deteriorated further in recent months, with rising unemployment, grinding poverty and daily blackouts that last for hours.
The protest campaign is also meant to spotlight Palestinian demands for a "right of return" to what is now Israel.
The prospect of more protests and Palestinian casualties in coming weeks could also place Israel on the defensive.
At the United Nations, Secretary-General Antonio Guterres called for an independent investigation, while Security Council members urged restraint on both sides. The council didn't decide on any action or joint message after an emergency meeting called by Kuwait Friday evening.
Abbas, the West Bank-based leader, renewed a call for international protection of Palestinians.
Palestinian Ambassador Riyad Mansour said he was disappointed the Security Council didn't coalesce to condemn what he called a "heinous massacre" of peaceful demonstrators, or to support his call to provide protection for Palestinian civilians.
"We expect the Security Council to shoulder its responsibility" and "defuse this volatile situation, which clearly constitutes a threat to international peace and security," Mansour said.
Israeli Ambassador Danny Danon said "the international community must not be deceived" by what he termed "a well-organized and violent terror-gathering" under the banner of a peaceful march.
"The Palestinians sunk to a new deceitful low so that they could use the U.N. to spread lies about Israel" while its representatives weren't there because of the Passover holiday, Danon said in a statement.
Some Security Council members suggested an investigation and emphasized that Israel should ensure force is only used proportionally. Some also made a point of noting Israel's security concerns and calling on demonstrators to avoid violence.
They all expressed alarm at the flare-up of conflict in a volatile region.
"The situation is extremely worrisome," said Swedish deputy Ambassador Carl Skau. Equatorial Guinea's ambassador, Anatolio Ndong Mba, warned that continuing violence could "escalate out of control and could further imperil what is already a very delicate situation" in Gaza.
The U.S., which often complains about what it sees as anti-Israel bias at the U.N., urged all involved in the conflict to lower tensions.
"Bad actors who use protests as a cover to incite violence endanger innocent lives," added Walter Miller, an adviser at Washingtontarget="_blank"'>