U.S. President Donald Trump solemnly paid tribute on Tuesday to the six million Jews killed during the Holocaust, calling on the world to never forget “history’s darkest hour.”

On a visit to the Holocaust memorial Yad Vashem, the president and first lady Melania Trump laid a wreath on a stone slab under which ashes from some of those killed in concentration camps are buried. They were joined by Israeli Prime Minister Benjamin Netanyahu and his wife, Sara, as well as Mr. Trump’s daughter Ivanka and son—in—law Jared Kushner, who are both White House senior advisers.

U.S. President Donald Trump, first lady Melania Trump and daughter Ivanka Trump, left, meet with Pope Francis, Wednesday, May 24, 2017, at the Vatican. As is tradition, the pope and president then exchanged gifts. Mr. Trump’s visit to the Eternal City comes after two stops in the Middle East where he visited the cradles of Islam and Judaism. Trump, midway through his grueling nine-day maiden international journey, called upon the pontiff at the Vatican early Wednesday where the two had a private 30-minute meeting laden with religious symbolism and ancient protocol. The president greeted Francis in Sala del Tronetto, the room of the little throne, on the second floor of Apostolic Palace Wednesday morning. Mr. Trump is the 13th president to visit the Vatican and, as part of his tour, he will view the Sistine Chapel. Donald Trump and his wife Melania are welcomed by Prefect of the Papal Household, Mons. Georg Gaenswein, as he arrives at the San Damaso courtyard for his private audience with Pope Francis, at the Vatican, Wednesday, May 24, 2017. U.S. President Donald Trump visits the Western Wall, Monday, May 22, 2017, in Jerusalem. He toured the Church of the Holy Sepulchre, which by Christian tradition is where Jesus was crucified and the location of his tomb. Wearing a black skullcap, he became the first sitting president to visit the Western Wall in Jerusalem’s Old City, the most holy site at which Jews can pray. Melania Trump touches the Western Wall, Judaism's holiest prayer site, in Jerusalem's Old City Monday, May 22, 2017. U.S. President Donald Trump (L) embraces Israel's Prime Minister Benjamin Netanyahu after his remarks at the Israel Museum in Jerusalem May 23, 2017. Trump reaffirmed his commitment to strong ties with the nation’s longtime ally and urged both the Israelis and the Palestinians to begin the process of reaching a peace deal. U.S. President Donald Trump and first lady Melania lay a wreath during a ceremony commemorating the six million Jews killed by the Nazis in the Holocaust, in the Hall of Remembrance at Yad Vashem Holocaust memorial in Jerusalem May 23, 2017. They were joined by Israeli Prime Minister Benjamin Netanyahu and his wife, Sara, as well as Trump’s daughter Ivanka and son-in-law Jared Kushner, who are both White House senior advisers. A still image taken from video shows Yad Vashem Chairman Avner Shalev presenting to U.S. President Donald Trump and first lady Melania a token of remembrance, an exact replica of the original Holocaust-era personal album that belonged to Ester Goldstein, who perished in the Holocaust, at Yad Vashem Holocaust memorial in Jerusalem May 23, 2017. U.S. President Donald Trump (2nd L), senior advisor Jared Kushner (3rd L), first lady Melania Trump (C) and Ivanka Trump, the president's daughter, listens to Rabbi Shmuel Rabinovitch (R) during a visit to the Western Wall, the holiest site where Jews can pray, in Jerusalem’s Old City on May 22, 2017. U.S. President Donald Trump and first lady Melania Trump walk in a procession to the Church of the Holy Sepulchre in Jerusalem May 22, 2017. White House senior advisor Jared Kushner (C) talks to his wife Ivanka Trump during a welcoming ceremony for her father U.S. President Donald Trump at Ben Gurion International Airport in Tel Aviv, Israel May 22, 2017. First lady Melania Trump visits GE All women business process service center in Riyadh, Saudi Arabia, May 21, 2017. In Saudi Arabia, Donald Trump addressed dozens of Arab leaders and urged them to fight extremists at home and isolate Iran, which he depicted as menace to the region. U.S. first lady Melania Trump speaks with Saudi Arabia's Crown Prince Muhammad bin Nayef during an arrival ceremony for U.S. President Donald Trump at the Royal Court in Riyadh, Saudi Arabia May 20, 2017. President Donald Trump holds a sword and dances with traditional dancers during a welcome ceremony at Murabba Palace, Saturday, May 20, 2017, in Riyadh.

Mr. Trump spoke on his fourth and final day in the West Asia. Earlier on Tuesday, his motorcade crossed through the barrier surrounding biblical Bethlehem for a meeting with Palestinian Authority President Mahmoud Abbas, where he pressed for progress on the dormant peace process.

If Israel and the Palestinians can forge an agreement, it can “begin a process of peace all throughout the Middle East,” Mr. Trump said.

Mr. Abbas said he was keen to “keep the door open to dialogue with our Israeli neighbours.” He reiterated the Palestinians’ demands, including establishing a capital in East Jerusalem, territory Israel claims as well, insisting that “our problem is not with the Jewish religion, it’s with the occupation and settlements, and with Israel not recognizing the state of Palestine.”

Condemns Manchester attack

Mr. Trump also condemned Monday night’s deadly explosion at a concert in England, calling those who carried out the attack “evil losers.”

“The terrorists and extremists and those who give them aid and comfort must be driven out from our society forever,” Mr. Trump said. “This wicked ideology must be obliterated.”

“So many young, beautiful innocent people living and enjoying their lives, murdered by evil losers in life,” Mr. Trump said, echoing the theme he presented during his meetings with Arab leaders in Riyadh, Saudi Arabia.

Mr. Trump declared that he would not call the attackers “monsters,” a term he believes they would prefer, instead choosing “losers,” a long-time favourite Mr. Trump insult and one he has directed at comedian Rosie O’Donnell, Cher and others.

Pays visit to Western Wall

Mr. Trump’s visit to Jerusalem has been laden with religious symbolism. He toured the Church of the Holy Sepulchre, which by Christian tradition is where Jesus was crucified and the location of his tomb. Wearing a black skullcap, he became the first sitting president to visit the Western Wall in Jerusalem’s Old City, the most holy site at which Jews can pray.

Mr. Trump was also joined at the wall by his family, who separated by gender to pray. The president and Mr. Kushner visited one side, while the first daughter and first lady visited a portion of the site reserved for women. Mr. Trump approached alone and placed his hand on the stone.

The visit raised questions about whether the U.S. would indicate the site is Israeli territory. The U.S. has never recognized Israeli sovereignty over parts of the Old City seized in the 1967 war.

The White House struggled to answer the question. Ambassador to the United Nations Nikki Haley declared the site part of Israel, while U.S. Secretary of State Rex Tillerson on Monday dodged the question. Mr. Trump himself never commented.