While South Africa and Turkey recalled their ambassadors to Israel because of the USA decision that has been widely criticised by its Western allies, some African countries sent representatives to witness the official opening of the United States embassy in disputed Jerusalem.
Police and the Israeli military deployed massively.
"We're far from any kind of resolution to the problems, and it could be a very tumultuous summer in the Middle East", he says.
The dead included eight children under the age of 16, according to the Palestinian envoy to the United Nations. The United States setting up an Embassy there purposefully undermines the Palestinian position and makes peace less likely.
US President Donald Trump also commented on the embassy's opening, but not on the protests. Hamas leaders have called for the protests to continue beyond Monday, however. "May God bless this embassy".
Iran decried "a day of great shame" over the deaths of dozens of Palestinians protesting Monday's controversial move of the U.S. embassy to Jerusalem.
"What was opened today in Jerusalem is not the us embassy but an Israeli settlers' post", Palestinian President Mahmoud Abbas said. "It was a barbaric massacre in Gaza today". He described Trump's move as the "slap of the century", and said the US could no longer be considered a neutral broker in Israeli-Palestinian peace talks now - or in the future.
Ardern said the Government had not spoken directly to the US, or US Ambassador, following the deaths.
A long-time Palestinian negotiator told CBS News he would like to see other countries step in to play a bigger role in the peace process.
There will also be many funerals in Gaza for those killed in the protests, each one likely to be attended by huge crowds and the focus of more fury.
Mansour cited the macabre juxtaposition of smiling faces at the embassy ceremony and a scene of anger, terror and death at the Gaza border.
"This action is legally null and void".
They are "alarmed by the disproportionate use of force displayed by the Israeli security forces against Palestinian demonstrators".
A 21-year-old and a 29-year-old were among the first killed by Israeli soldiers, according to the Gaza Health Ministry.
At least 6,000 people converged on Monday in central Istanbul to denounce the inauguration ceremony and the killings of at least 55 Palestinians by Israeli forces in Gaza - in what marked the bloodiest day in the besieged coastal enclave since the 2014 war.
"East Jerusalem is occupied land".
Later in the day, Israeli leaders and a U.S. delegation including Treasury Secretary Steven Mnuchin and President Donald Trump's daughter and son-in-law, Ivanka Trump and Jared Kushner, were due to attend the opening of the embassy. US Treasury Secretary Steve Mnuchin unveiled the US seal.
"I think this is a pattern which we will be witnessing in the next period with Trump's increasing bellicosity towards Iran".
He said Trump made good on his promise.
Israeli Prime Minister Benjamin Netanyahu praised the move, calling it historic.
"This is a great day".
The Trump administration expressed its support for Israel's show of force against the Palestinians.
The protests were supposed to end on May 14, the day on the Gregorian calendar when Israel became an independent state 70 years ago, which the Arab world calls the Nakba, or catastrophe.
"Of all the things President Trump could have done, doing this (embassy move) is the strongest signal he could send to the Israeli people", South Carolina's Graham said.