UN Secretary General Ban Ki-moon said on Sunday that he was “shocked” by the shooting attack at the Jewish Museum in Brussels on Saturday that claimed four lives.

“The Secretary-General notes that, while the investigation is ongoing, the location of the attack points to a possible anti-Semitic motivation behind it,” a spokesperson for the secretary general said in a statement, adding that the UN chief sends his condolences to the families of the victims.

“[The Secretary General] reiterates his strong condemnation of all forms of racism, racial discrimination, xenophobia and related intolerance and trusts that Belgian authorities will do everything possible to bring the perpetrator or perpetrators of this crime to justice swiftly,” he went on.

Earlier Sunday, Pope Francis — who is on a three-day regional tour in Jordan, the West Bank and Israel – said he was deeply saddened by the deadly shooting attack.

“I am profoundly saddened, my thoughts go out to those who lost their lives in the attack in Brussels,” the 77-year-old pontiff said as he arrived in Israel on the final leg of a three-day Middle East tour.

“I entrust the victims to God,” he said.

Belgian police at the site of a shooting at the Jewish Museum in Brussels, on Saturday, May 24, 2014. (photo credit: AP Photo/Yves Logghe)

Belgian police at the site of a shooting at the Jewish Museum in Brussels, on Saturday, May 24, 2014. (photo credit: AP Photo/Yves Logghe)

On Sunday, the deadly attack claimed its fourth victim as Alexandre Strens, a young man who was critically injured by gunshot died of his wounds. An Israeli couple and a French woman were killed at the scene on Saturday.

Joel Rubinfeld, head of the Belgian League against Anti-Semitism, told AFP that Strens, who was in his early 20s and worked as a receptionist at the museum.

The shooting, which took place in central Brussels on Saturday afternoon, drew condemnation from European leaders, and was blamed by Prime Minister Benjamin Netanyahu on a growing wave of anti-Semitism sweeping Europe.

Belgian prosecutors on Sunday said they were looking for a lone suspect in the lethal weekend shooting spree.

Deputy prosecutor Ine Van Wymersch said the suspect “probably acted alone, was armed and well prepared.”

Police had detained one suspect late Saturday but he was soon released and is now considered a witness.

A motive was not yet given, but the government has said it had the hallmarks of an anti-Semitic attack.

“Nobody has claimed this attack. All options are still open,” Van Wymersch said.

This videograb released on May 25, 2014, by the Belgian federal police on demand of Brussels' king prosecutor, shows the suspect of the killings in the Jewish Museum on May 24,2014 in Brussels. (photo credit: AFP PHOTO/BELGA/BELGIAN FEDERAL POLICE/HANDOUT)

This videograb released on May 25, 2014, by the Belgian federal police on demand of Brussels’ king prosecutor, shows the suspect of the killings in the Jewish Museum on May 24,2014 in Brussels. (photo credit: AFP PHOTO/BELGA/BELGIAN FEDERAL POLICE/HANDOUT)

The two Israelis killed in the deadly attack were identified late Sunday morning as Tel Aviv residents Mira and Emmanuel Riva, who were on an organized, private walking tour of Brussels when the shooting took place.

Belgian Jewish community leader Maurice Sosnowski said Sunday that the museum was not protected like other Jewish centers in Brussels because it is not exclusively a Jewish community structure, and therefore it was “an easy target.”

“This was a pre-planned attack, it wasn’t something that could be improvised. The victims were shot at the entrance to the museum. It seems that there were one or two shooters; the modus operandi reminds us of the shooting in Toulouse,” he added, referring to the March 2012 attack in which four people were killed by a motorcycle-riding gunman outside a Jewish school in the French city.

The Saturday terror shooting has caused a great deal of worry in the Belgium Jewish community and other communities in Europe, Sosnowski said, and noted that “security has been increased to the highest level at all Jewish centers. The local authorities are putting all efforts into solving this case.”

On Sunday morning, before the weekly cabinet meeting, Netanyahu, who had condemned the attack immediately after it occurred on Saturday, noted “the hatred the Jewish people are witnessing in these days.” He praised Pope Francis, who is currently on a visit to Israel and the Palestinian Authority, for his “firm stand against anti-Semitism.”

It was the first fatal attack on a Jewish center since the early 1980s in Belgium, home to some 40,000 Jews, roughly half of them in Brussels, the remainder in the port city of Antwerp.