U.S. President Donald Trump and his top aides on Monday hailed the opening of the new U.S. Embassy in Jerusalem as a "great day," a position that roiled the Arab world and fuelled deadly protests along the Israeli-Palestinian border.

The move ends — at least for now — the U.S. chances of becoming a neutral peace broker in the Middle East. And while the approach was swiftly condemned by Muslim world leaders, Trump's new policy appeases a powerful pro-Israeli lobby within the Republican Party.

According to the Gaza Health Ministry, 55 Palestinians, including six children, were killed by Israeli forces during mass protests along the Gaza border on Monday. It was the deadliest day there since a devastating 2014 cross-border war.

A female Palestinian demonstrator gestures during a protest at the Israel-Gaza border on Monday. (Mohammed Salem/Reuters)

The ministry also said 1,204 Palestinians were shot and wounded, including 116 who were in serious or critical condition. It said about 1,200 others suffered other types of injuries, including from tear gas.

In a show of anger fuelled by the embassy move, protesters set tires on fire, sending plumes of black smoke into the air, and hurled firebombs and stones toward Israeli troops across the border. Later on Monday, Israeli forces fired from tanks, sending protesters fleeing to take cover.

The Israeli military said its troops came under fire in some areas, and said protesters tried to break through the border fence, although they did not succeed in breaching it.

An Israeli soldier carries a hose as he walks in a burning field on the Israeli side of the border fence between Israel and Gaza on Monday. (Amir Cohen/Reuters)

The army also said it used airstrikes and tank fire against Hamas targets in Gaza after squads of gunmen opened fire and tried to plant bombs along the border.

In a video message played at the embassy inauguration, Trump said he remains committed to "facilitating a lasting peace agreement" between Israelis and Palestinians.

"A great day for Israel!" Trump tweeted earlier Monday.

However, Monday's steadily climbing death toll and wall-to-wall condemnation of the embassy move by the Arab world raised new doubts about Trump's ambitions to broker what he once said would be the Mideast "deal of the century."

Palestinian President Mahmoud Abbas lashed out at the U.S., saying he "will not accept" any peace deal proposed by the Trump administration.

Saeb Erekat, a senior Abbas aide, said Trump had violated a promise to hold off on moving the embassy to give peace talks a chance and that his administration is "based on lies."

Abbas also urged the international community to condemn what he said were "massacres" carried out by Israeli troops.

But Israeli Prime Minister Benjamin Netanyahu said Israel's actions on the Gaza border were self-defence against the enclave's ruling Hamas group.

Israeli Prime Minister Benjamin Netanyahu delivers a speech during the opening ceremony of the new U.S. Embassy in Jerusalem on Monday. (Sebastian Scheiner/Associated Press)

"Every country has an obligation to defend its borders," Netanyahu wrote on Twitter. "The Hamas terrorist organization

declares it intends to destroy Israel and sends thousands to breach the border fence in order to achieve this goal. We will continue to act with determination to protect our sovereignty and citizens."

At the embassy ceremony in Jerusalem, Trump's son-in-law and chief Mideast adviser Jared Kushner also placed the blame for the violence on the Gaza protesters.

"As we have seen from the protests of the last month and even today those provoking violence are part of the problem and not part of the solution," he said.

During his speech at the opening ceremony, White House senior adviser Jared Kushner praised his father-in-law, U.S. President Donald Trump, for following through on his campaign promise to move the U.S. Embassy to Jerusalem from Tel Aviv. (Ronen Zvulun/Reuters)

Kushner and Trump's daughter Ivanka led a high-powered American delegation to the embassy opening that also included the treasury secretary and four Republican senators.

The new embassy will temporarily operate from an existing U.S. consulate, until a decision has been made on a permanent location.

In Gaza, the Hamas-led protest was meant to be the biggest yet in a weeks-long campaign against a decade-old blockade of the territory. The Israeli military estimated a turnout of about 40,000, saying this fell short of what Hamas had hoped for.

The march was also directed at the inauguration of the embassy.

Moving the embassy from Tel Aviv to Jerusalem — a key Trump campaign promise — infuriated the Palestinians, who seek east Jerusalem as a future capital.

Monday marked the biggest showdown in years between Israel's military and Gaza's Hamas rulers along the volatile border. The sides have largely observed a ceasefire since the 2014 war — their third in a decade.

A protester is detained by Israeli security forces in Jerusalem during a demonstration against the opening of the new U.S. Embassy there on Monday. (Ammar Awad/Reuters)

The protest was the culmination of a campaign, led by Hamas and fuelled by despair among Gaza's two million people, to break the blockade of the territory imposed by Israel and Egypt after Hamas seized control of Gaza in 2007. Since weekly border marches began in late March, 85 Palestinian protesters have been killed and more than 2,500 wounded by Israeli army fire. Hamas said four members, including three security men, were among the dead Monday.

Ismail Radwan, a senior Hamas figure, said the mass border protests against Israel will continue "until the rights of the Palestinian people are achieved."

"Moving the U.S. Embassy to Jerusalem will be a disaster for the American administration and a black day in the history of the American people because they are partners with the occupation and its aggression against the Palestinian people," he added.

Throughout the day, sirens wailed as the wounded were carried to nearby ambulances. Groups of young activists repeatedly approached the fence, but were quickly scattered by gunfire and tear gas.

Lt.-Col. Jonathan Conricus, an Israeli military spokesperson, said the army had set up additional "layers" of security in and around communities near the border to defend Israeli civilians. He said there already had been several "significant attempts" to break through the fence. The army said aircraft targeted a Hamas post in northern Gaza after Israeli troops came under fire.

A general view of the entrance to the new U.S. Embassy in Jerusalem on Monday. The U.S. has transformed its consulate, with the Trump administration planning to build a permanent complex elsewhere. (Ronen Zvulun/Reuters)

The timing of Monday's events was deeply symbolic to Israel and the Palestinians.

The U.S. said it chose the date to coincide with the 70th anniversary of Israel's establishment.

But it also marks the anniversary of what Palestinians call their "nakba," or catastrophe, a reference to the uprooting of hundreds of thousands who fled or were expelled during the 1948 war that followed Israel's creation.

A majority of Gaza's two million people are descendants of refugees, and the protests have been billed as the Great March of Return to long-lost homes in what is now Israel.

Palestinian protesters carry an injured man shot by Israeli troops during a protest Monday at the border with Israel. (Khalil Hamra/Associated Press)

Protester Mohammed Hamami, a 40-year-old civil servant, attended the march with his mother and five children. "Today we are here to send a message to Israel and its allies that we will never give up on our land," he said.

Clouds of black smoke from burning tires rose into the air. Protesters have used the thick smoke as cover against Israeli snipers perched on high sand berms on the other side of the border. The Israeli army accuses Hamas of using the protests as cover to plan or carry out attacks.

Israel captured east Jerusalem in the 1967 Mideast war and annexed it in a move not recognized by the international community. The Palestinians seek the city's eastern half as the capital of a future state.

Netanyahu has repeatedly praised Trump's decision to upend decades of U.S. policy by recognizing Jerusalem as Israel's capital.

Although Trump has said his declaration does not set the final borders of the city, it is seen by both Israel and the Palestinians as taking Israel's side in the most sensitive issue in their conflict.

Only two countries, Guatemala and Paraguay, have said they will follow suit. Most of the world, including Canada, maintains embassies in Tel Aviv, saying the Jerusalem issue must first be resolved.