The United Nations on Friday condemned what it called an "unlawful air strike" by Israel on a refugee camp in the occupied West Bank that the Palestinian health ministry said killed 18 people the previous day.

"The strike is part of a highly concerning pattern of unlawful use of force by ISF (Israeli security forces) during military-like operations in the West Bank that have caused widespread harm to Palestinians and significant damage to buildings and infrastructure," the United Nations rights office said in a statement.

"This incident is another clear example of ISF's systematic resort to lethal force in the West Bank that is frequently unnecessary, disproportionate, and therefore unlawful," the office said, as it called for an independent probe into the incident.

"The levelling of an entire building filled with people via aerial bombing shows flagrant disregard for Israel's obligations."

The Israeli army confirmed the strike on the refugee camp of Tulkarem in the northern West Bank on Thursday, describing it as a joint operation carried out by the Shin Bet internal security service and the air force.

It said the strike had killed a Hamas leader in Tulkarem, Zahi Yaser Abd al-Razeq Oufi.

A source within the Palestinian security services told AFP that the air raid was the deadliest in the West Bank since 2000. (AFP)