Police had already confirmed the deaths of two settlers in their 60s and a 20-year-old woman civilian on national service.
The fourth person killed was a young Jewish settler who died in the attack at the entrance to the Kedumim settlement west of the Palestinian city of Nablus.
The Palestinian bomber set off his explosives next to an Israeli car at a petrol station at the entrance to the settlement, according to Israeli media reports.
According to the Palestine Media Centre, the bomber was Ahmad Masharkah, 24, from the Hebron area in southern West Bank. He had previously been arrested by the Palestinian National Authority and was in Jericho prison until March 14 when he was among the men set loose during an Israeli occupation forces raid that demolished the prison.
The victims are believed to have offered a lift to the Palestinian, who was hitch-hiking while disguised as an ultra-Orthodox Jew, reports say.
Claim of responsibility
A new offshoot of the Fatah movement from the Balata refugee camp in nearby Nablus said it carried out the attack. The group called itself Kateb al-Shahid Chamuda.
Al-Manar TV in Lebanon broadcast a claim of responsibility from the Al Aqsa Martyrs' Brigades, an offshoot of Fatah, which is headed by Mahmoud Abbas, the Palestinian president.
The last bombing of a similar nature in the West Bank was on December 29 at an Israeli army checkpoint. An Israeli soldier and two Palestinians were killed in addition to the bomber.
This was the first such attack claimed by a group other than Islamic Jihad since a ceasefire was declared in February 2005.
Kedoumim, in the middle of the West Bank, is the northernmost Israeli settlement after Israel's evacuation of four settlements in the summer.