At least 17 Palestinians have been killed and 2000 injured in clashes with Israeli soldiers during protests at the Gaza border, Palestinian representative to the UN Riyad Mansour said.
Israeli officials estimated tens of thousands of Palestinian protesters marched in Gaza on Friday towards the border fence between Israel and Gaza during a protest called the "Great March of Return".
The march quickly turned bloody as Palestinian protesters and Israeli military clashed along the fence, CNN reported on Saturday.
The aim of the protest was to assert what Palestinians regard as their "right to return" to towns and villages from which their families fled, or were driven out, when the state of Israel was created in 1948.
Palestinian President Mahmoud Abbas said the Israeli authorities bore "full responsibility" for the deaths and declared Saturday as a day of mourning. Thousands of people were attending the funerals.
UN Secretary-General António Guterres called for an independent inquiry into the deaths and the UN Security Council condemned the violence after an emergency session. UN deputy political affairs chief Taye-Brook Zerihoun told the Council: "Israel must uphold its responsibilities under international human rights and humanitarian law."
The Palestinian leadership also accused the US of obstructing a UN resolution to denounce the Israeli aggression.
"The US provided a cover for Israel to continue its aggression on the Palestinian people and encourage it to defy international legitimacy resolutions that aim at ending the occupation," said Nabil Abu Rudeineh, spokesperson of the Palestinian President said.
A health ministry spokesman told Efe news that about 2,000 other Palestinians were injured during the protests called by Hamas in observance of Land Day on Friday, which symbolises the demand of Palestinian refugees and their descendants to be allowed to return to their homeland.
More than half of Gaza's 2 million people are refugees or their descendants, according to the UN.
The Israeli Defence Forces (IDF) said in a statement that "17,000 Palestinians are rioting in five locations along the Gaza Strip security fence".
Israel announced earlier this week that 100 snipers would be posted along the Gaza border.
Other Palestinian factions have joined Hamas in promoting the "Great Return March", which envisions maintaining a presence of hundreds of protesters along the Gaza border between now and May 15, when Palestinians commemorate what they call the Nakba (Catastrophe), referring to the exile and dispossession of Arabs that accompanied the founding of Israel in 1948.
The Land Day tradition was spurred by the events of March 30, 1976, when Israeli forces fatally shot six Palestinian protesters.
Thousands attended funerals of those killed — two were buried yesterday — with mourners holding Palestinian flags and some chanting "revenge" and firing into the air.
The armed wing of Hamas, said that five of those killed were members who were participating "in popular events side-by-side with their people."
"Where are you, Arabs? Where are you, Muslims?" mourners chanted at one funeral, calling on the Arab and Muslim world to intervene.
A general strike was also being held in both the Gaza Strip and the occupied West Bank.
Minor clashes between Israeli forces and Palestinians broke out in Hebron, while a small protest was held in Nablus, both in the West Bank.
Unverified videos were being shared online, including one appearing to show a protester being shot while running with a tyre.
No casualties were reported among Israelis.
Human Rights Watch criticised Israel's actions.
"Israeli allegations of violence by some protesters do not change the fact that using lethal force is banned by international law except to meet an imminent threat to life," the New York-based group said, calling the number of killed and wounded "shocking."
Israel's arch-foe Iran, a longstanding supporters of Hamas, condemned the "shameful" killing of protesters and mocked the fact that it happened as Israeli Jews prepared to mark Passover. Agencies