The United States inaugurated on Monday its embassy to Israel in the holy city of Jerusalem, drawing international outcry amid violent clashes on the Gaza border.
The opening was accompanied by violent Gaza border clashes that left at least 50 Palestinians dead and 2,000 injured from Israeli fire.
The clashes, which left hundreds of Palestinians wounded, erupted before a White House delegation and Israeli officials opened the embassy at an inauguration ceremony in Jerusalem and continued throughout the day.
Palestinian President Mahmud Abbas condemned Israeli "massacres", declaring three days of mourning,
He said "the US is no longer a mediator in the Middle East," and the new embassy was tantamount to "a new American settler outpost" in Jerusalem.
The Hamas movement vowed protests would continue.
The US has lost its role as mediator in the Middle East by moving its embassy in Israel to Jerusalem, Turkish President Recep Tayyip Erdogan said in London on Monday.
"With its latest step, America has chosen to be a part of the problem, not a solution, and lost its mediator role in the Middle East peace process," Erdogan told the Chatham House international affairs think-tank.
The bloodshed along Gaza's border is an "abhorrent violation" of human rights, Amnesty International said.
"We are witnessing an abhorrent violation of international law and human rights in Gaza... This must end immediately," the London-based human rights group said on Twitter.
British Prime Minister Theresa May's spokesman urged "calm and restraint" in the Gaza Strip.
"The prime minister had made her views clear in December that we disagreed with the decision (to move the US embassy). We believe it's unhelpful in terms of prospects for peace in the region."
"The British embassy to Israel is based in Tel Aviv and we have no plans to move it."
France also spoke out against the US move, saying along with many other critics that it violated "unambiguous" international law and UN Security Council resolutions.
Russian Foreign Minister Sergei Lavrov reiterated Moscow's objection to the move, saying: "We firmly believe that it is inappropriate to unilaterally revise the decisions of the international community in this way."
Moroccan King Mohammed VI wrote in a letter to Abbas that he was "monitoring with concern" the US recognition of Jerusalem as the Israeli capital, the MAP news agency reported.
Like Belgian Foreign Minister Didier Reynders, the Moroccan king denounced Washington's "unilateral decision".
The Egyptian foreign ministry, in a statement expressing "strong denunciation" of Israel's use of force against Palestinian civilians, said Cairo "totally supports the legitimate rights of the Palestinian people, and first and foremost its right to an independent state with East Jerusalem as its capital."
The UN Security Council will convene on Tuesday to address the situation in Gaza.
