The US officially relocated its Embassy to Jerusalem on Monday, formally upending decades of American foreign policy in a move that was met with clashes and protests along the Israeli-Gaza border.

At least 43 Palestinians were killed in Gaza as deadly protests took place ahead of and during the ceremony in Jerusalem — making it the deadliest day there since the 2014 Gaza war.

President Donald Trump did not attend the ceremony in Jerusalem’s Arnona neighborhood, but in a video message broadcast at the event he congratulated Israel, saying the opening had been “a long time coming.”

“Today, Jerusalem is the seam of Israel’s government. It is the home of the Israeli legislature and the Israeli supreme court and Israel’s prime minister and president. Israel is a sovereign nation with the right like every other sovereign nation to determine its own capital, yet for many years, we failed to acknowledge the obvious, the plain reality that Israel’s capital is Jerusalem,” Trump said in the pre-recorded remarks.

“As I said in December, our greatest hope is for peace.” he added.

The opening of the Embassy happened a day after Israel celebrated Jerusalem Day, marking what Israelis consider the reunification of the city.

Speaking at the ceremony, the Israeli Prime Minister Netanyahu hailed the alliance between America and Israel as “stronger than ever.”

“What a glorious day, remember this moment. This is history,” he said.

“President Trump by recognising history, you have made history. All of us are deeply moved, all of us are deeply grateful.”

Outside the embassy, police and protesters clashed as tensions ran high.

Fourteen protesters were arrested for confronting police officers and interrupting public order, Jerusalem police said.

Trump’s decision to declare Jerusalem the capital of Israel and relocate the Embassy from Tel Aviv is contentious for Palestinians, who hope to claim part of the city as their future capital.

The city is also home to deeply holy sites for Jews and Christians. The issue has been so thorny that international negotiators had left the question of Jerusalem to the final stages of any peace deal.

The decision has been widely criticized by leaders in the Middle East.

Iran’s Foreign Minister Javad Zarif accused the US of “ignoring international regulations and global agreements.”

Rami Hamdallah, the Palestinian Authority’s Prime Minister, also criticized the decision, claiming the date of the move, the day before “Nakba” (also called Catastrophe, marking more than 700,000 Palestinians driven from, or fled their homes during the Arab-Israeli war that accompanied the creation of the State of Israel in 1948) showed “disrespect” for the peace process.

The Arab League said it would hold an “extraordinary meeting” on Wednesday to discuss the “illegal” move, the Middle East News Agency MENA reported on Monday.

International condemnation also came from France, which said it “disapproves” of the relocation.

“This decision contravenes international law and in particular the resolutions of the Security Council and the UN General Assembly,” a statement from the French Foreign Ministry read.