The United States on Friday condemned the attack on a home in the Arab village of Duma as a "vicious terrorist attack".
An 18-month-old Palestinian Arab baby was killed in the firebomb attack, believed to be the work of Jewish extremists.
A statement from the State Department quoted by AFP urged Israel to "apprehend the murderers" and called on both sides to "avoid escalating tensions in the wake of this tragic incident."
State Department spokesman Mark Toner said Washington "condemns in the strongest possible terms last night's vicious terrorist attack in the Palestinian village of Duma.
"We convey our profound condolences to the Dawabsha family and extend our prayers for a full recovery to those injured," he added.
Four family members of the one-and-a-half year-old were transferred to Israeli hospitals for treatment after the attack, which the Defense Ministry, IDF, Prime Minister Binyamin Netanyahu, and greater political establishment condemned as "despicable."
Netanyahu later on Friday paid a visit to the family of the child, Ali Dawabsha, at the Chaim Sheba Medical Center at Tel Hashomer.
Speaking following the visit, Netanyahu strongly denounced the "brutal" attack and said he had called Palestinian Authority chairman Mahmoud Abbas to vow Israel would track down the killers.
"I just came from the bedside of four-year old Ahmed Sa'ed. Sixty percent of his body is burned. We're doing everything we can to save this young boy, give him a life," Netanyahu said. "His two parents are in other parts of the Israeli health system. We're trying to give them the best treatment to save their lives."
"When you stand next to the bed of this small child, and his infant brother had been so brutally murdered, we're shocked, we're outraged. We condemn this. There is zero tolerance for terrorism wherever it comes from, whatever side of the fence it comes from, we have to fight it and fight it together."
"I spoke to President Abu Mazen right before I entered the hospital. I told him of this visit and of Israel's absolute commitment to find the perpetrators, bring them to justice," Netanyahu continued, while calling for calm.
"We have to calm the spirits and recommit ourselves to our joint battle against terrorism and extremism. It's something that all parts of the Israeli government and all parts of Israeli society agree on. It's important that we make a common cause with our Palestinian neighbors to give ourselves a better future – a future free of violence, free of terror, a future of peace."
(Arutz Sheva’s North American desk is keeping you updated until the start of Shabbat in New York. The time posted automatically on all Arutz Sheva articles, however, is Israeli time.)