A West Bank mosque which was gutted by fire on Monday was most probably attacked by arsonists, Israeli fire-fighters say.
Officials believe arsonists broke into the mosque in Lubban al-Sharqiya, near Nablus, and set it on fire using paper.
Palestinian leader Mahmoud Abbas has accused Jewish settlers of starting the fire, warning the attack could jeopardise peace talks due to begin.
Initial reports said an electrical short circuit may have caused the fire.
"The investigation showed in most probability that this was a case of arson," the spokesman for Israeli fire service in the West Bank Capt Jacky Binyamini told the BBC on Thursday.
"It is important to note that the investigation was carried out in full co-operation with investigators from the Palestinian fire fighting services," the spokesperson said.
A report by the fire-fighters is expected to be submitted to Israeli police on Thursday, reports said.
The investigation ruled out the possibility that there was an electrical short circuit that caused the fire, Israel's Yehdiot Aharanot newspaper reported.
Israeli police say the investigation is still under way, and the cause of the fire has not yet been determined.
The mosque is close to three Jewish settlements.
The attack came as US Middle East envoy George Mitchell returned to the region, attempting to restart Israeli-Palestinian peace talks.
"This criminal attack threatens efforts to revive the peace process," said Mr Abbas in a statement earlier this week.
He pointed the finger of blame at Israel, adding that "the Israeli army protects the settlers".
Hamas, which is opposed to peace talks with Israel, has said the mosque attack is "the first fruit of the pointless negotiations," Reuters reported.
Israel had warned Palestinians in the West Bank that there is a risk of local settlers attacking homes in the area after the Israeli army demolished houses in a settlement near Nablus, Palestinian officials say.
The West Bank has seen a series of attacks on mosques in recent months.
Last month, another mosque in the village of Huwara near Nablus was vandalised by Hebrew graffiti. Palestinian residents blamed activists from three nearby Jewish settlements.
In January, Israeli police arrested settlers as part of investigations into an arson attack on a West Bank mosque in 2009.