Three people were severely injured when an explosive device detonated Friday morning near the Ein Bubin spring next to town of Dolev.
The victims include a 46-year-old father and his 18-year-old daughter and 20-year-old son.
The daughter, Rina Shnerb, who was declared to be in critical condition, died of her wounds a short time later.
Magen David Adom (MDA) volunteers are at the scene providing the wounded with medical care.
All of the victims have been evacuated via helicopter to medical centers.
IDF forces are chasing a suspicious vehicle which escaped the scene and is believed to be the vehicle of the terrorists who threw the explosive device. The possibility that the explosive was a grenade thrown at people hiking in the spring is also being investigated.
An IDF statement on Twitter read: "We received a report of an explosive incident near the town of Dolev in the Ephraim Brigade's region. It seems three people were injured. Details are being investigated, and IDF soldiers are searching the area."
Later, the IDF said: "Following the previous report regarding a terror attack near the community of Dolev, northwest of Ramallah, three civilians who were in a nearby spring were injured in an IED blast."
"The circumstances of the attack are being investigated.
"One of the civilians is being treated at the scene while the remaining two were evacuated by an IDF helicopter to a hospital for further medical treatment.
"The Commanding Officer of the Central Command, the Commanding Officer of the Judea and Samaria Division and additional officers are in the field and are assessing the situation. IDF troops have been deployed and are searching the area. The troops are blocking roads and enhancing the defense of the area."
MDA tweeted: "At 10:15 we received a report via the MDA hotline in the Jerusalem area regarding an explosion near a spring in Dolev. Initial reports said there were at least two people seriously injured."
A later tweet read: "Regarding the incident near Dolev: MDA medics and paramedics are administering medical aid to three seriously injured individuals, including a 46-year-old man, a 21-year-old man, and an 18-year-old woman. We will continue to update."
MDA Paramedic Shlomo Perl reported from the scene: "When we arrived at the scene what we saw was horrifying. We saw 3 injured laying on the ground. A 46-year old man, fully conscious, had sustained injuries to his upper body. Next to him was a 20-year old man with injuries to his upper limbs and upper body and a 17-year old teenager with multi-system trauma."
"We administered initial medical checks and provided them with life-saving treatment which included stopping the bleeding and providing medications. We evacuated the 46-year-old and 20-year-old man via the MICU and evacuated them to a military helicopter that landed close by, which took them to the hospital. The teenager is being treated at the scene by our paramedics and IDF medical forces."
An MDA spokesperson said: "MDA EMTs and Paramedics together with IDF medical teams are treating and evacuating in a military helicopter to Hadassah Ein Kerem Hospital a 46-year-old and a 20-year-old male in serious condition, fully conscious with major injuries caused by the explosion and shrapnel. The 17-year-old girl is still being treated in critical condition."